If a Lead-acid battery is left in a state of deep unload for a long period of time, a sulphation will take place.

Part of the sulphuric acid is combined with the lead that comes from the plates in order to create lead sulphate. If the battery is not refilled with water periodically, part of the plates may be exposed to the air and the process will be accelerated. The lead sulphate covers the plates in such a way that the electrolyte cannot go into them. This means an irreversible loss of the battery’s capacity which, even adding water, cannot be recovered.