Would you have thought that you have bought yourself another advantage with a start-stop system, but only if you kept the vehicle long enough? We are talking about an Absorent Glass Mat accumulator. Because it lasts longer. Ours is already in its twelfth year.

This is called 'cycle stability' when a battery (we're sticking with the actually wrong term) can withstand many discharges/charges. With the AMG battery, this is guaranteed by a glass mat that encloses the electrolyte. The acid is therefore no longer present in its original liquid state.

This has relatively little to do with another weakness of batteries, which is that they are self-discharging. In winter, depending on the temperature and equipage, you are dependent on a battery that is at least half full anyway. If it also loses around 0.5 percent of its nominal capacity or more per day, you can calculate how long it will take for the vehicle to stop starting.

In addition, there are all kinds of consumers, such as the anti-theft alarm system. Some electric cars even have cameras ready to photograph, which react to almost everyone who approaches the car. In addition, many of these cars also consume electricity when they are stationary, but hopefully this is at the expense of the high-voltage battery.

No, it's not just a lack of comfort when such an engine no longer reaches its required starting speed. Then the limit of deep discharge is quickly reached, which experts set higher than laypeople. One speaks of 'sulphating' the lead plates, a layer of lead sulphate that covers the positive plates.

Even if that doesn't completely knock off the battery, there is often at least a loss of usable capacity. So when charging, not so much lead sulphate (PbSO₄) can move from the plus to the minus plates. Of these, only lead (Pb) arrives. The acid residue (SO₄) increases the acidity of the electrolyte.

To do this, PbSO₄ must become H₂SO₄. The hydrogen comes from the water content of the electrolyte, and the oxygen released in the process migrates to the positive plate. This is the reason why, at least in the past, it was possible to test the individual cells for the density of their electrolyte. 1.28 kg/litre meant fully charged, 1.12 kg/litre uncharged.

Actually quite easy to remember: With a charged battery, the positive pole due to lead oxide and the negative pole due to only lead are different and after discharge both are the same, namely consisting of lead sulphate. So there is a certain logic in charging the battery more often than absolutely necessary. You should only do this permanently with electrically monitoring chargers, because the battery should not always be completely full.

It gets worse when the water content in the electrolyte also still freezes. Incidentally, the may only be supplemented with distilled water. If you find a proven way around the sticker to open the individual cells, you could also refill water if necessary. This is impossible with AGM batteries anyway.

Only distilled water is ever refilled, never e.g. acid. The only exception at that time were dry pre-charged batteries. But the liquid to be filled was there present. We have long included classic cars, which are very often put out of operation in the winter. You should combine the removal of the battery (observe the radio code if necessary) with an intensive corrosion test.

Should a new battery then be necessary, the voltage is the least of the problems because 12V is universal, at least in the car sector. Actually, the maximum discharge current on the label should also be observed, but it is usually completely sufficient. The capacity is a value that may also be exceeded. However, this is usually not necessary.

On the contrary, because more capacity also means more installation space and that is what matters if you want to install a new one. In addition to length, width and height, this also applies to the attachment. You are well advised to take the old battery with you when you buy a new one. You don't have to dispose of them yourself and sometimes even get paid for it. One has hardly any problems with the installation space, but possibly with the possible attachment of a 12V lithium ion battery. But the prices are high and the shelf life rather indeterminate.