Storage of the battery (Mercedes-Benz C-Class W202)

Batteries that have not been used for a long time discharge themselves and, in addition, their plates may be sulfated. If these batteries are charged with a fast charger, they do not absorb the charging current or, due to the so-called surface charge, are "fully charged" too early. They seem to be faulty. But before considering these batteries faulty, they should be checked.

Check the electrolyte density. If the electrolyte density in all cells differs by no more than 0.04 g/ml, then this battery can be charged with a standard charger.

If the density in one or two adjacent cells deviates more significantly (more than 0.04 g/ml), then the battery has an internal short circuit and is faulty.

After charging, test the battery under load. If it does not reach the specified values, it is faulty.

To prevent battery aging, the stored battery should be recharged every three months.

(Full article available on the resource: MercedesMan)