Does the maintenance of lead still make sense?



For lead batteries (colloquially also lead batteries or in connection with cars starter batteries or car batteries) the same principles apply as for all accumulators. If you are not familiar with the basic structure and mode of operation of rechargeable batteries, read this page for you Accumulators suggested, on the basic information about the Construction of rechargeable batteries are included. You can also see an explanation of Technical terms relating to battery technology and an overview of the various Find battery types.

General / structure

The Lead-acid batteries are standard equipment in every car with a combustion engine. It is often referred to as a battery, car battery, motorcycle battery, starter battery or lead battery. The correct and unambiguous designation lead accumulator or lead accumulator for short stems from the fact that both electrodes are made of lead or a lead alloy and that it is rechargeable. Sulfuric acid serves as the electrolyte. When charged, the positive pole plate consists of lead dioxide (PbO2) and the negative of bare lead (Pb). When discharging, finely divided lead sulphate (PbSO4) forms on both plates, which is converted back into lead dioxide or lead during charging.

Due to the highly corrosive electrolyte, lead accumulators are potentially dangerous in the event of a defect and, if not disposed of properly, anything but environmentally friendly, as lead is a poisonous heavy metal. They must therefore be recycled, which has been mandatory for car batteries in Germany for a long time. Lead batteries are comparatively heavy, bulky and have a low current-carrying capacity compared to other types of batteries of the same size. In addition, the self-discharge of a starter battery at room temperature is relatively high at 5 to 10% per month (lead-gel batteries about half or even less). With a self-discharge rate of 10%, the remaining charge after 6 months is 50% and after 12 months it is only 30% of the capacity. However, lead-acid batteries are comparatively cheap, robust, very easy to charge and, above all, can also be used at clear temperatures below zero, which is why, despite their numerous disadvantages, they are still used exclusively as starter batteries in the automotive sector. For reasons of weight and space, other types of batteries are preferably used as drive batteries in hybrid vehicles.

Starter batteries used in the automotive sector have lead electrodes that are designed to be extremely porous in order to achieve a large surface area per volume in order to reduce the high internal resistance typical of lead batteries. This is achieved in that the electrode plate is basically not a plate, but rather looks like a grid. During production, this lead grid is coated with a paste made from lead particles (negative electrode) or lead dioxide particles (positive electrode), which form the actual electrode material. Due to the large surface area of ​​the extremely large number of small particles, which act like a sponge, the car battery can deliver much more electricity than with a simple sheet metal as an electrode, which is a basic requirement for a successful cold start. In addition, a comparatively large capacity is achieved with a small volume. But it also has a very decisive disadvantage: Since the lead electrode is not unlike a sponge, tiny parts of the electrode crumble off with each charging / discharging process, because the chemical conversion of the electrodes leads to mechanical stresses. The reason is that lead sulfate takes up more space than lead or lead oxide. The volume of the particles in the electrode therefore increases when discharging and decreases again when charging. On the one hand, the crumbling reduces the effective surface, which leads to a higher internal resistance and a reduced capacity. On the other hand, so-called battery sludge forms, which settles on the ground. In the case of a car battery, the electrodes do not reach all the way to the bottom, so that the partially conductive battery sludge can safely settle down. However, if it reaches the electrodes, a short circuit can occur, rendering the affected cell and thus the entire battery unusable. If you discharge the battery heavily (in the worst case up to the capacity limit) and then recharge it, quite a lot of material crumbles off, which extremely shortens its service life.

Due to the electrode structure, starter batteries are designed to deliver high currents for a very short time. The typical value of the starter current ("starter") in a mediocre 4-cylinder gasoline engine is 150 to 200 A, with a multiple of this being required at clear temperatures below zero. In the case of diesel engines, it is generally higher due to the higher compression of the engine and the associated higher drive power. As already indicated above, starter batteries generally do not like it when you take a lot of charge from them, because the electrodes then crumble away quickly. This is also not the case with regular operation: The current is very high, but only a small amount of charge is taken from the battery in the few seconds to start the motor (with 2 seconds and 200 A it is only 0.1 Ah), and it is charged again immediately after the engine has started. Normally, a starter battery should not be charged with more than 3% of its nominal capacity, whereby the recommended maximum is 10%. Anything beyond that is extremely unhealthy for the battery and should be avoided if possible. For this reason, the vehicle manufacturer does not base the selection of the battery on the capacity but rather on the so-called cold test current, which is always specified on the battery, but in contrast to the basically meaningless capacity specification (you cannot use the capacity quickly without the battery to destroy) has unfortunately not yet made it into the consciousness of the motorist. The cold test current states how much current the starter battery can deliver when new at a battery temperature of -18 ° C for a period of 30 s without the voltage dropping below 9 V. The is the criterion that really counts with starter batteries.

In the case of very extreme short-distance operation or if the generator ("alternator") is defective, the battery is not sufficiently charged and is more or less constantly in a half to almost completely discharged state. Almost empty starter batteries "draw" a great deal of current from the on-board network when the engine is running, which means that the charging current is much too high and, as a result, many more parts of the electrodes crumble off during the charging process than with gentle charging. If a battery has to remain in a strongly discharged state for days, large lead sulfate crystals form on the electrodes from the many finely divided lead sulfate crystals, which are very difficult to restore due to their poor electrical conductivity (see Sulfation). This is therefore equivalent to a reduction in capacity that can no longer be fully reversed. Together with the battery sludge, these are the main reasons why lead-acid batteries usually do not last very long in extremely short-haul cars. This can be mitigated by regularly charging the battery with a charger if the vehicle is frequently used for short trips, ideally every evening. The same problem occurs with vehicles with a stop / start system, since the engine is very often automatically switched off and restarted in city traffic. The problem of insufficient charge is usually countered here by using a battery sensor, which prevents the engine from being switched off automatically if the battery is insufficiently charged. The problem of the electrodes crumbling off due to the very frequent engine starts and thus a large number of cycles can be countered by using significantly more cycle-resistant batteries such as batteries in EFB (=E.nhanced F.looded B.attery) or AGM technology (=A.adsorbent Glet The aim is always to keep the crumbling particles in place mechanically.

It is really bad if a conventional car battery is used for a purpose other than its intended purpose (e.g. as a supposedly inexpensive alternative to batteries specially designed for solar systems or electric drives) and operated far outside of its specification, for example by repeatedly discharging it beyond the maximum specified depth of discharge of mostly 10%. The formation of sludge is very high here, which has a very negative effect on its service life. It only survives a discharge to the limit of its capacity a few times. For this very reason, there are special solar accumulators ("solar batteries") for solar systems, in which the design ensures that they can withstand strong discharge cycles much better and that they also have less self-discharge. The benefits of solar batteries are bought with a larger installation space, more electrode material, additional measures such as glass fiber fleece, etc. and thus a significantly higher price, which is comparatively high, not least because of the very small number of units compared to the millions of car batteries. But even deep cycle solar batteries should never be completely discharged if possible. The same applies to so-called drive batteries, which are also optimized for cycle stability with a comparatively high depth of discharge.

Since car batteries age quickly when they have to give up a high percentage of charge, it is also not nonsensical - as recommended in the past - to use a battery with a larger capacity if you have an auxiliary heater, radio devices (e.g. in taxis), music systems in your vehicle or other additional consumers that are used when the engine is not running. The higher capacity is by no means needed to meet the electricity requirements of the auxiliary heating or other additional consumers, because you would need about 5 A for the auxiliary heating and another 5 A for the fan (to convey the warm air into the interior) a heating time of a whole hour only 10 Ah (on the other hand only 1/4 to 1/2 hour are necessary with a sufficiently powerful auxiliary heater). This would not pose any major problems even to the smallest conventional battery in the automotive sector with 36 Ah. However, including the subsequent engine start, it would discharge a good quarter, which is not good for its service life. A significantly larger battery is discharged less in percentage terms and thanks to the fact that it does not break down as quickly. As a pleasant side effect, you also have more reserves if the battery clearly loses its capacity at the end of its service life. Incidentally, the widespread claim that a small generator ("alternator") has problems with a "big car battery" or is even damaged is nonsensical in this context. Generators installed as standard in today's vehicles have an output of 1500 W and often even more. This corresponds to a current of more than 100 A. A commercial car battery cannot absorb such a high charging current at all, unless it is very strongly discharged; The problem with charging lead-acid batteries is more likely to get enough power and thus charge into the battery in short-distance traffic in order to achieve a reasonably short charging time. The charging current is seldom much more than 10 A, even with a large 100 Ah battery. The generator cannot be damaged anyway, because the voltage drops automatically if the generator cannot supply enough power. Incidentally, this can often happen while driving, because at idle speed the maximum current output of a generator is very low. If many consumers (rear window and seat heating, lighting, fog lamps, ventilation at the highest level, etc.) are switched on, the battery will even deliver electricity instead of being charged when the engine is idling. If you are attentive, you can recognize this in vehicles with conventional halogen lighting by the slight fluctuations in the color and intensity of the headlights. It is better to use a larger starter battery, but it is always better to supply the auxiliary heater and fan or other additional consumers with power via an additional cycle-proof battery; then the starter battery only has to supply the starter current, as in cars without auxiliary heating, and this thanks to a significantly longer service life. Unfortunately, the cabling for this operating mode is somewhat complex, and the additional battery must also be accommodated somewhere, which is why this is unfortunately only rarely done. If you shy away from this effort, you should at least not use the cheapest NoName product for the starter battery, but rather a cycle-proof battery in EFB (=E.nhanced F.looded B.attery) or better AGM technology (=A.adsorbent Glet, as is customary for vehicles with a stop / start system. The costs for an EFB or AGM battery are a good bit higher than for normal starter batteries, but the bottom line is that it is worthwhile due to the significantly longer service life in this operating mode. A higher capacity of the starter battery - as recommended earlier - is then of course not necessary.

Next the starter batteries for vehicles of all kinds with internal combustion engines are also other types of lead batteries. The above-mentioned EFB or AGM technology holds the material of the plate mechanically in place by means of a fabric made of e.g. polyester (EFB) or a glass fleece (AGM) and thus largely prevents the plates from crumbling off at a greater depth of discharge. The glass fleece of the AGM batteries also binds the acid and holds it in place through capillary action, so to speak Avoids problems caused by acid stratification. In addition, such a battery can be operated largely independently of its position. In so-called lead gel batteries, the diluted sulfuric acid is fixed in a gel. Because the electrolyte is not liquid, lead-acid batteries can be operated in any position - in contrast to AGM batteries, even overhead, which is completely unthinkable with lead-acid batteries with liquid electrolytes. What all these batteries have in common is that the respective design measures significantly increase both the maximum depth of discharge and the cycle stability compared to starter batteries. Because of these improved properties, they are often used as emergency power supplies for alarm systems, medical devices or uninterruptible power supplies (UPS). Other areas of application are, for example, solar technology for bridging the sunless period ("solar battery"), mobile homes or boats for the purpose of supplying power when the engine is not running, electrical drives and many more. Unfortunately, such batteries are significantly more expensive than starter batteries of the same capacity due to the higher material requirements and the lower number of pieces. When used as intended, they have a considerably longer service life than if starter batteries are misused for such applications.

Charging lead-acid batteries

Lead-acid batteries are sensitive to deep discharge. Even a single deep discharge can render the battery unusable, even if it is immediately recharged. Charging itself is very simple: you supply it with a current that is not too high (usually 1/20 to 1/10 of the capacity specification) and switch when it reaches approx. 2.4 V per cell (i.e. just below the gassing voltage, which, however, is is strongly temperature-dependent) into a recharge phase with a constant voltage of 13.8 V, for example, during which the battery is fully charged for a few hours (e.g. overnight). The value of approximately 13.8 V is the voltage at which a fully charged battery is no longer charged, but only the self-discharge is compensated. With this voltage, it can therefore be charged for a very long time without causing damage. Another method is to apply a voltage just below the gassing voltage (usually 14.4 V for chargers that are not temperature-compensated) and to stop charging when the charging current has dropped below 2% of the capacity specification. Example for a 60 Ah battery with 12 V nominal voltage: Charging current between 3 and 6 A with switch-off at a charging current below 1.2 A. There are a number of other charging methods, some of which are only suitable for very special battery types: For stationary ones Batteries that can be refilled with water, for example, are deliberately made to gas for a limited time so that the electrolyte is well mixed by the gas development to avoid the undesired Avoid acid stratification. Batteries without the possibility of topping up with water can, however, be rendered unusable very quickly with such a charging process.

The gassing voltage is the voltage from which the battery is practically no longer charged, but almost the entire current splits the water in the electrolyte into hydrogen and oxygen and thus decomposes it. This gas mixture explodes violently even in small quantities with the slightest spark, which is why charging can only be carried out outdoors or in well-ventilated rooms. Inexpensive chargers not only do not have an automatic switch-off when the gassing voltage is reached, but also allow a battery to always gas through pulsating DC voltage with a high peak value. Not too much overcharging does not cause too much damage to batteries that have access to the individual cells, but water is lost.If you have overcharged the battery, you have to restore the old liquid level by topping up with distilled water, if that is possible at all - the "calcium batteries", which are widely marketed as maintenance-free, normally no longer have any maintenance openings through which you can refill water. Under no circumstances may you use commercially available "battery acid" to refill; this is only intended for filling so-called "dry pre-charged" lead-acid batteries (i.e. batteries that are delivered without acid for shipping reasons). Since only water was split into hydrogen and oxygen during overcharging, but the acid remained unaffected and was also not consumed, only distilled water has to be refilled. If you top up with "battery acid", there is too much sulfuric acid in the battery fluid, which firstly reduces the conductivity and thus the power supply capacity, and secondly promotes the formation of large sulfate crystals (see Sulfation), which reduce the capacity.

The on-board network voltage and thus the charging voltage of the battery is still not temperature-compensated in many vehicles. As a result, at a high battery temperature (the gassing voltage is lower than at a low temperature), the on-board electrical system voltage can be higher than the gassing voltage. Then the water in the battery is broken down into oxygen and hydrogen and consumed in the process. The gassing is not that bad, but it does lower the fluid level. If the liquid level is so low for a long time that the plates are no longer completely surrounded by acid, the dry plate parts lose their power storage capacity, so that the capacity remains reduced even after topping up with water. Problems in winter are therefore mostly solved by negligent care in summer. It is therefore advisable to check the acid level of the battery more often, especially in summer, and to top up with water if necessary. However, this problem only occurs when the battery temperature is very high and the battery is being charged at the same time, which is rarely the case. While driving, the cooling air ensures that the battery does not get too warm. Really high battery temperatures only occur if you park a car that has run hot for a long time with high load and high speed at high outside temperatures, because then the engine heat is not efficiently dissipated by the airstream or the fan, but the hot air accumulates under the bonnet and then heats up the battery. At first this is not critical because the battery is not charged when the engine is not running. The worst case from a battery point of view is when, after about half an hour or a full hour, i.e. when the battery temperature has reached its maximum, a new journey begins and the battery is then charged, i.e. overcharged. The cooling air can only cool the warm battery very slowly, which is why overcharging takes a long time. Vehicles in which the battery is not in the engine compartment but e.g. in the trunk do not have this problem, of course.

Unless your car battery is of a "maintenance-free" type, you can usually access the electrolyte by removing 6 screw plugs or a plastic strip and, if necessary, you can easily top up with distilled water. You should check every 1 to 2 months (if you drive a lot more often) that the fluid level is still high enough. Make absolutely sure that no electrically conductive parts can fall into the battery; a short circuit within the cell with gigantic currents would put a spectacular end to his life. In addition, the sudden development of heat would cause hot acid to squirt out, which can lead to severe burns and blindness. In the case of transparent batteries, the target level is usually indicated by a mark on the side of the battery. If this is missing, the liquid level should be approx. 1 cm above the upper edge of the plates. If it is lower, you should top up with distilled or demineralized water as soon as possible in the interests of a long service life.

If you have discharged or even deeply discharged your battery, e.g. by forgetting to switch off the lighting, you should never charge it with a quick charger. Deep discharging is bad enough, and the high charging current would damage it even more. Rather, it must be slowly nursed back to life with a low charging current. Therefore, even if it takes a long time, you should only charge it with a low current. This is what he likes best in normal operation. As a rule of thumb, the current should not exceed a tenth of the battery capacity, but it can be less. In the case of a battery with a capacity of 60 Ah, for example, the charging current should therefore be 6 A or less. If you want to be prepared for any eventuality and are therefore thinking of purchasing a charger, you should leave high-performance devices on the shelf for the reasons mentioned and buy one with low power but automatic shutdown ("electronic charge control" or "microprocessor-controlled") . Modern chargers do not need a large transformer like the one shown in Figure 1, but are equipped with a so-called switching regulator, in which the transformer can be considerably smaller due to the high switching frequency with the same current. You are familiar with this technology, e.g. as a power supply unit for notebooks. Such chargers usually have an electronic charge control thanks to microprocessor control and, because of the much smaller and therefore cheaper transformers, are still hardly more expensive than the old-fashioned, thick boxes in the simplest design that are still sold.

Image 1: Simple charger for lead-acid batteries

As you can see in Figure 1, the normal chargers, which you can buy for little money in the accessory trade, have an extremely simple structure. They only consist of a sheet steel housing, a transformer, a rectifier, a very simple measuring device and a fuse holder. At its output, the rectifier does not deliver a direct voltage, as it would be useful for gentle charging, but only a rectified alternating voltage, as shown in Figure 2:

Fig. 2: Rectified alternating voltage

The peak value of the voltage US is usually approx. 20 V with only a low current, which means that the rms value Ueff shown in red is in the range around 13.5 to 14 V. By periodically exceeding the gassing voltage of the accumulator, an accumulator gasses when using such chargers. This is always the case when the charging voltage exceeds the red straight line. Thanks to its relatively low internal resistance, an empty battery loads the charger so much that the voltage of the charger remains below the gassing voltage, but the charging current decreases well before it is fully charged, which also reduces the load on the charger. As a result, the charging voltage periodically exceeds the gassing voltage. This is not particularly good for the battery, even if the water, which is split into water and oxygen, is replaced by filling with distilled water after charging. Since the battery is almost always guest with such chargers, it is very difficult to determine when the battery is really fully charged. Therefore, when you buy a charger, you should definitely buy one with a so-called electronic charge control. If you are well versed in electronics, you can also buy a very inexpensive one and retrofit it with a little electronics that limit the voltage to the desired end-of-charge voltage. I have equipped the device shown above for very little money with an electrolytic capacitor for voltage smoothing and a current-limited voltage regulator that delivers max. 4 A and max. 14.8 V. Since a battery begins to gas very slightly at this voltage between 80% and 90% charge level (it always does this, it is normal and even useful to avoid acid stratification, see sulfation), a battery with such a charger must not be used Charge it indefinitely, but must switch it off as soon as the charging current has dropped below 2% of the capacity specification. Otherwise, the recommendation is to buy a charger with switched-mode power supply technology that is small, light, inexpensive and equipped with electronic charge control. This not only reduces the light gassing to a minimum shortly before full charge, but can also remain connected as long as you like, i.e. it does not have to be monitored.

If you have actually discharged the battery very far, charging it overnight is easily enough, even with low power, to be able to start your vehicle again in the morning. Even with a high assumed starter current of 500 A and a very long start-up time of 10 s, only a charge of 1.4 Ah is required, while with a low 2 A charging current and a charging time of 8 hours, 16 Ah can be charged into the battery. It is highly recommended to continue charging at the earliest opportunity until the battery is fully charged.

If you have suffered the mishap of a discharged battery overnight, you have to drive to work quickly in the morning and you cannot jump-start another vehicle, you do not have to fully charge the battery. It is enough to charge it enough to start the engine. As long as the battery is not frozen (see below) and your car normally starts immediately, you can start an attempt after just 5 minutes with a charging current of 4 A; but really real 5 minutes wait and no "felt 5 minutes", which in reality are only 30 seconds! It is essential that you switch off all power consumers (lights, rear window heating, ventilation, seat heating, air conditioning or auxiliary heating, music system, etc.) while charging and during the start attempt, remove the ignition key from the ignition lock and close all doors so that the interior lighting does not come on . If the engine has not started within 2 seconds at the latest or if you notice that the starter has slackened due to a lack of power, switch off the ignition immediately and continue charging, at least 10 minutes before you try again. Avoid long "messing around", because this only discharges the battery unnecessarily, which extends the charging time, and also ensures that the spark plugs are wet, which in the worst case scenario means that the engine will not start at all without special measures. Do not forget to disconnect the charger before attempting to start, because simple chargers in particular are not short-circuit-proof and the high starter current comes very close to a short-circuit.

After a successful start, you should only switch on the electricity consumers that are really necessary (i.e. no rear window heating, no seat heating, no fog lights, etc.) and drive off immediately, whereby you should, as an exception, avoid an excessively low-speed driving style. If you have to stop at traffic lights or the like, it is advisable to step on the gas with your foot so much that the engine rotates at least 1500 revolutions per minute, even if the person next to you or behind is upset about it. Otherwise there is a risk that the generator will deliver less electricity than is consumed. As a result, the battery would not be charged but rather discharged, which is why the motor threatens to go out if the red phase persists. With the procedure described, the battery should be charged enough to start the engine for the way back, even on a relatively short drive, provided that the (renewed?) Deep discharge was not the fatal blow for him. Back at home, it is best to give it a gentle full charge with a charger or, on the way back, drive at least a longer distance at not too low a speed across the country with as few electrical consumers as possible switched on in order to at least partially charge it, and then find out more where you can have it fully charged as soon as possible (workshop, petrol station, loaned charger, etc.) and, if available, do not use the auxiliary heater and other large consumers such as seat heating, fog lights or rear window heating (the latter, if available) until fully charged absolutely necessary, only use very briefly and only while driving). Should the battery fail again the next morning despite this special treatment, you can be fairly certain that it has reached the end of its life. A measurement of the acid density in a fully charged state (see next chapter) provides final certainty in this regard.

If you put your vehicle out of use for the winter, it is advisable to pay a little attention to the battery during this time in the interests of a long service life. If possible, you should remove the battery and overwinter it in a frost-free, dry place. In vehicles with a carburettor that are not very old, disconnecting can lead to problems (loss of the adaptation values ​​of the engine control, entering the security code of the radio etc.), which is why removing it is not always practical and the battery is better left in the vehicle. In both cases, it is ideal if the battery is kept fully charged by a special small charger with a low current. This is countered by the fact that such a charger then consumes electricity 24 hours a day, significantly more than the battery needs to maintain the charge. In practice, it makes sense to recharge the battery around every 2-4 weeks and then disconnect the charger. For some years now, devices have been available that cyclically discharge the batteries a little and then recharge them. What still makes limited sense with NiCd batteries is counterproductive with car and motorcycle batteries because of the increased accumulation of battery sludge, which is why it is better to limit yourself to only fully charging the battery on a regular basis.

Lead-acid battery charge level

With With the help of a hydrometer, popularly known as a battery acid lifter, which you can buy for little money in specialist shops, you can measure the density of the electrolyte, i.e. the "battery acid", provided that the electrolyte in your battery is accessible, which unfortunately is increasingly rare. You have to be careful not to suck in too much or too little acid. The little swimmer must be able to swim freely and unhindered, i.e. he must neither hit the top due to too much acid in the acid siphon (and thereby indicate too low a density) nor lie on the bottom due to too little acid (which means he must indicate too high a density). With a new lead-acid battery, you can read directly on the hydrometer whether the battery is fully charged (1.28 kg / l), completely empty (1.12 kg / l) or charged to a certain percentage. These values ​​are only valid if the target fluid level is maintained (top up with distilled water if necessary) and the battery is new. It is important that the density is measured in all cells and that it is the same in all cells with a low tolerance. With a lead-acid battery that has been in use for some time, the specified 1.28 kg / l will no longer be achieved despite being fully charged. This is completely normal, because with increasing age, an ever larger proportion of lead sulphate can no longer be converted back into pure lead (negative plate) or lead dioxide (positive plate) plus sulfuric acid during charging. Since part of the sulfuric acid remains bound as lead sulphate, the "battery water" contains correspondingly less sulfuric acid. And since sulfuric acid has a higher density than water, the density of the solution decreases if you remove some of the sulfuric acid from it. In a test with a 1 year old battery, I was only able to measure 1.26 kg / l despite being fully charged with an electronic charger, see picture on the left. With a fully charged battery, the acid density is an indicator of its performance. However, you cannot regenerate the battery by subsequently increasing the acid density, for example by adding concentrated sulfuric acid, because the reduced acid density is only a symptom and in no way the cause of the decreasing capacity. If acid is added, the conductivity of the electrolyte would decrease, so that the maximum current decreases and the engine may no longer start, especially when it is cold.

Please be very careful when checking the acid density and wear protective goggles and, if possible, old clothing. Because even a small splash of sulfuric acid can burn a hole in clothing or skin and, in the worst case, lead to blindness if it gets into the eyes. If the worst comes to the worst, rinse the affected areas immediately with plenty of water. If acid has got into your eyes, you must immediately rinse them out with plenty of water and it is imperative that you consult an ophthalmologist immediately after rinsing. If you cannot go to this as quickly as possible on your own, notify the emergency services immediately, because your eyesight is at stake. Do you remember the case of the Iranians, who were blinded and disfigured by a disdained admirer with sulfuric acid and who fought for the right to blind their tormentor with sulfuric acid in 2011 before an Iranian court, but then renounced enforcement? The sad example of this woman shows that even small amounts of sulfuric acid can cause immense damage to health. When handling sulfuric acid, therefore, precautionary measures are not a luxury but absolutely necessary.Because of these dangers, you should only determine the density of the battery acid if it is absolutely necessary. After use, rinse the hydrometer under plenty of running water and rinse the inside well so that the storage location is not damaged by acid residues.

Sulphation of lead batteries

As already explained above, when a lead battery is discharged, lead sulphate forms on both plates. According to this, sulphation always takes place when discharging, because that is simply the way a lead-acid battery works. The catchphrase sulfation, which providers of windy devices (more on that in a moment) like to use as a bogeyman and synonym for an early "battery death", is completely wrong, because, to put it simply, there is no electricity without sulfation. On the other hand, it is correct that the formation of relatively large lead sulfate crystals is accompanied by a reduction in capacity. Because, to put it bluntly, you can no longer access them electrically, because they conduct electricity only very poorly. They can therefore no longer be removed even with special charging or discharging processes, and also not with chemical additives. Due to the large lead sulfate crystals, an ever increasing proportion of the area of ​​the lead plates is no longer available for energy storage. At the same time, the sulfuric acid bound in the crystals decreases the acid concentration and thus the acid density, because the sulphate formation binds part of the battery acid to the plates, so that the acid density decreases with increasing sulphation.

What can you do about so-called sulfation? Basically, as already mentioned, sulphate formation is a completely normal process: even in the ideal case, lead sulphate forms on both plates when discharging. When charging, this is completely converted back into lead dioxide (positive plate) and lead (negative plate). In reality, the reconversion no longer works when relatively large lead sulfate crystals have formed. The aim is not to prevent the formation of lead sulphate per se (as is often wrongly read) but rather to prevent the formation of large crystals. When discharging, tiny, finely divided crystals tend to form, which can easily be re-formed, especially when a high discharge current is flowing. Large crystals tend to form when standing around because crystals need time to grow. On the other hand, large crystals tend to form when there is already a lot of lead sulfate, i.e. when the battery is heavily discharged. You probably know that from sugar crystals: Large crystals separate from a sugar solution only if you let them grow very slowly and carefully. If you constantly create turbulence in the sugar solution, only many small crystals will form, and if you lower the sugar concentration in the solution, almost no crystals will form. A high discharge current in the battery ensures a high level of microturbulence where the lead sulphate is formed, which makes it difficult for large crystals to form. If no external current flows, however, large crystals can develop because then only the very low self-discharge current flows inside the battery compared to the usual charging and discharging currents.

The said sulphate layers can no longer be removed with any miracle device that applies special current pulses to the battery. The assertion that the sulfate crystals can be "broken open" and thus "reversed" is not tenable either in theory or in practice. Lead sulphate conducts electricity very poorly, which is why it is no longer possible to separate the lead from the sulphate with electricity. This is completely independent of the current strength or the pulse shape or frequency with which you are working. In addition, each time the engine is started, the battery is loaded with a significantly stronger and longer current pulse than with such devices. When mid-displacement engines are started in summer, a current of the order of 150 to 200 A flows for a few seconds, and even more in winter. In addition, if you have not switched on too many consumers, the charging current is quite high shortly after starting the engine and, depending on the charge level of the battery, is often in the range of 50 to 100 A in the first few seconds Sulphation cannot be reversed, how should it work with extremely short pulses of only a few microseconds in duration (1 μs = 0.00001 s) and the comparatively low current with which these miracle devices work? In any case, a capacity-increasing effect has never been proven by an independent body (i.e. paid jubilation Persians not counted). Apart from that, one should consider how much such a miracle device costs and how much a new battery, which one cannot avoid buying in the long term anyway.

You can't destroy large sulfate crystals, but you can preventive do something, namely avoid the formation of these large sulfate crystals as far as possible: Since small crystals grow into large ones over time, one should convert all lead sulfate into lead dioxide (positive plate) or lead (negative plate) every now and then, i.e. remove it while it is still works. This can be achieved quite easily by simply fully charging the battery. In the car, however, lead-acid batteries almost never reach the state that they are fully charged, especially in winter. One reason for this is that the charging voltage required for a full charge increases when it is cold, but the on-board voltage in most cars is constant and has been selected so low that the battery is not overcharged even in summer to avoid gassing. As a result, the voltage in winter is too low to really fully charge the battery. Few cars have temperature-dependent voltage regulation, in which the on-board electrical system voltage is increased at low temperatures. Another reason is that the generator has to supply many consumers in winter (lighting, rear window heating, heated seats, fans, etc.), which means that significantly less electricity is left for charging than in summer. It looks better in summer, but even then, except for extreme long-distance vehicles, the batteries are often almost fully charged, but only almost completely. The reason is that the travel time is usually simply too short to reach 100% charge. The missing few percent to fully charge are then precisely the small sulfate crystals that continue to grow undisturbed because they are never regressed and thus reduce the capacity. First of all, due to the electrical conductivity, the smallest crystals are always receded during charging and finally the larger ones, so that the same crystals are no longer regressed and can continue to grow until they are finally too big. If the capacity is reduced, the lead sulphate is never broken down elsewhere due to a lack of real full charge, which means that further large crystals are formed there, etc., until at some point the remaining capacity of the battery is no longer sufficient to start the engine.

It follows from this: If you want to extend the life of a lead-acid battery, you should regularly give it a real full charge with a charger, even if it is almost fully charged. The charger must be one with electronic charge control. A good rule of thumb is once a week in winter and once a month in summer; more often does not hurt, but makes more effort. Due to the temperature dependency of the cell voltage, charging should be carried out in an environment that is not too cold, otherwise the charging process will be terminated too early, as chargers only rarely have temperature compensation and therefore have a temperature sensor that has to be attached to the battery. Nevertheless, it is of course still much better to recharge even in freezing cold than to leave the battery half-discharged. With lead-acid batteries that are stored uncontacted, no current is drawn externally, but they only discharge through the inevitable self-discharge, which is comparatively slow. It is therefore sufficient if such batteries are only fully charged about once a month.

It is important to know that this approach only helps if it from the beginning, i.e. if the battery is still new, is carried out consistently. If the battery is already weak, it hardly has any effect. Then you can only extend its service life by a few days by external charging in order to have enough time to find an inexpensive source of supply for a (hopefully) high-quality replacement battery. Buying at the nearest gas station is likely to be the worst case in terms of price and buying in the nearest hardware store in terms of quality. Since a battery ages the most by just standing around, you should make sure when buying that the date of manufacture is under no circumstances more than 6 months in the past (it is better to be significantly shorter, the date of manufacture is unfortunately increasingly rare for car batteries), because regularly since manufacture it was definitely not charged. It is better to order a battery from a specialist retailer, who in my experience often sells branded batteries at a lower price than some hardware stores, and to wait a few days for a fresh battery to be delivered. Alternatively, you can also order branded batteries cheaply over the Internet, which may save you a lot of work.

Acid stratification

Another evil is the so-called acid stratification. This means that the acid concentration and thus the acid density is not the same everywhere in the battery, but more concentrated acid collects at the bottom due to its higher density (concentrated sulfuric acid is almost twice as heavy as water with the same volume), while less concentrated acid swims at the top . The acid stratification has the consequence that the battery is no longer fully charged and, in addition, the formation of large sulfate crystals is promoted by two mechanisms. Lead-fleece batteries, in which the acid has been made more or less stationary by means of a glass fiber mat, are only slightly affected by this effect. With lead-acid batteries, acid stratification is of course not an issue at all, as the electrolyte cannot move at all here.

Due to the special way in which car batteries operate, the acid stratification is created as follows: When the engine is started, a very high current flows for a short time, which, especially in winter, is not too far below the short-circuit current of the battery. With such a high current, even the smallest ohmic resistances play a role. The plate electrode has a noticeable ohmic resistance between the upper and lower edge, which is the reason that with a high extraction current, the upper part of the plate provides a significantly higher proportion of the total current than the lower. A direct consequence is that the acid density in the upper part of the battery drops more than at the bottom. When charging, however, the current is significantly lower, which is why the current distribution on the plate surface is considerably more homogeneous. Since the lower part had less charge when discharging than the upper part, it is also recharged more quickly and drives the terminal voltage of the battery up. The terminal voltage is thus higher than it corresponds to the actual total charge level of the battery. Due to the higher terminal voltage, the charging current decreases, which is why the battery can no longer be fully charged due to the limited charging time in the vehicle (after all, charging is only carried out while the engine is running, which is shorter than you think) and therefore shows a reduced capacity. While there is a high acid density in the lower area of ​​the battery, it is lower at the top because not all of the sulphate could be converted back there if it was not fully charged. The acid stratification is reinforced by the fact that concentrated sulfuric acid, which arises locally from the sulphate during charging, has a tendency, due to its high density, to sink downwards and collect there. The vibrations and rocking and rocking movements while driving help reduce acid stratification, but usually they are not enough to avoid it altogether due to the tight plate stratification and separators.

The acid stratification not only has the effect that the battery can no longer be fully charged. Rather, it damages the battery through two other mechanisms: The excessively high acid concentration in the lower area of ​​the battery leads to corrosion of the electrodes, i.e. lead sulphate is produced in the lower area of ​​the plates during rest breaks (cars usually stand around most of the time) despite being fully charged which grows into large crystals over time. In contrast, the upper area of ​​the plates is never fully charged, so that the lead sulphate finds the same paradisiacal state as in an empty battery, where it can also grow into large crystals. In the upper area, however, the formation of large sulfate crystals is superimposed on the fact that a relatively large amount of electrode material and thus also the sulfate crystals crumble off here, because the current density is high here and a strong discharge takes place locally, which promotes electrode wear.

The acid stratification can be reversed by ensuring that the electrolyte is thoroughly mixed. To do this, you could theoretically turn it upside down a few times for a few minutes each time and then back on your foot. In practice, this does not work because lead-acid batteries with liquid electrolyte have ventilation openings through which the acid would leak out from a certain angle. Incidentally, even closed batteries without the possibility of refilling with water have such ventilation openings. In addition, regularly removing the battery from the car would not really be effective. Fortunately, there is an electrical way to greatly reduce the acid stratification: You have to specifically overcharge the battery a little. First, the water is electrolytically decomposed in the area of ​​the lower plate parts, creating hydrogen and oxygen bubbles that rise upwards and ensure that the electrolyte is well mixed. At the same time, the upper plate areas are fully charged. This process is called equalizing charge. To do this, the battery is first fully charged conventionally. Then the charging voltage is increased for a limited time to e.g. 15.8 V to 16.2 V (assuming a battery temperature of 20 °) and charging is terminated as soon as the charging current has dropped below 1/20 of the value of the nominal capacity (e.g. with a 60 Ah battery to 3 A). In another equalizing charging process, instead of a constantly increased voltage, a constant current of 1/20 of the value of the nominal capacity is fed in and charging is terminated when the terminal voltage reaches the said voltage value. An equalization charge can also partially reverse the start of sulfation and equalize differences in the charge level of the various battery cells. In the case of batteries that can be topped up with water, it is advisable to carry out an equalization charge once a month. The electrolyte level should first be checked and, if necessary, topped up with water and only then should an equalization charge be carried out so that the electrolyte is well mixed after this measure (of course, checking again after charging cannot do any harm). With modern, so-called "maintenance-free" batteries (often referred to as "calcium batteries") you cannot top up with water, which is why you should not make an equalization charge, because otherwise you would drive out the devil (acid stratification) with the Beelzebub (water consumption).

Cold behavior of lead batteries

As already described above, the density of the electrolyte (sulfuric acid) changes with the state of charge. Unfortunately, the freezing point changes with the acid density. A fully charged lead battery with an acid density of 1.28 kg / l has a freezing point of a whopping -68 ° C. With an empty battery with an acid density of 1.12 kg / l, however, it is only -11 ° C. In winter in particular, a lot of electricity is required for lighting, rear window heating, etc., so that, especially in short-distance traffic, more electricity may be used than the generator can supply; In addition, the usable capacity is reduced at low temperatures. As a result, batteries that are no longer completely dewy are often permanently almost empty in winter and are therefore sensitive to frost. If you only drive short distances and park your vehicle outdoors, you should keep an eye on the acid density and, if necessary, remove the battery or charge it with a low current if it is announced that there is severe frost. Because when the battery freezes, cracks often form in the housing, through which the acid leaks out as soon as it thaws. When this happens in the vehicle, all metallic parts with which it comes in contact will corrode. If the battery is frozen, it emits absolutely no more current and the control lights do not even light up when the ignition is switched on. In this case, remove the battery as quickly as possible while it is still frozen and place it in a large plastic bowl in a warm place. If there is no leakage and no cracks are visible, you can try to charge it gently after it has completely thawed and then reinstall it. Otherwise you have to dispose of it (i.e. hand it in at a specialist retailer) and buy a new one. Be careful with the leaked acid!

If the acid density is permanently low and hardly increases even when fully charged, you can continue to use it until the battery dies, but it makes a lot of sense to replace it with a new one as soon as possible. Because it will soon fail anyway, preferably when you least need it, namely when it is cold, dark and uncomfortable and you are also in a hurry. If you have a lot of time in the morning, you can extend the service life by a few days or weeks with jump-start assistance, recharging, etc., but it makes much more sense to look for a new battery straight away. Because as long as your vehicle starts relatively smoothly, you still have the chance to visit several shops and find inexpensive yet high-quality replacements (the price differences are sometimes enormous). If the battery is finally flat, you have missed this chance and may have to accept the next best and therefore most likely expensive and qualitatively rather suboptimal offer. If you absolutely want to use up the old battery completely in the few days or weeks before it dies, which is not advisable because of the inconvenience involved and the amount of work involved in continually recharging, you should at least buy a new battery in good time. You should carry it with you in the fully charged state in the car and also do not forget the right tools for changing (try it out beforehand!) And a working flashlight to avoid standing in the middle of the pampas at night in freezing cold and not moving again, because the car does not start due to the dead battery. As I said: It is much easier on the nerves to install or have the new battery installed in good time and thus without great stress.