When a lead-acid battery is fully or partially, lead sulfate to form the electrodes.
If the battery is to keep a long term in the discharge, or very low state of charge of lead sulfate may be it is hard to convert lead sulfate to form large crystals, the charging process.
Make these crystals called sulphates and lead to permanent loss of capacity of the battery.
To avoid this problem lead-acid batteries, therefore can only be stored in a fully charged state and charge should add not self-discharge of battery.
To extend shelf life without charging, the battery should be kept in 10 ℃ or lower ° but electrolyte should not be allowed to freeze.
When the battery is fully charged the electrolyte of the sulfuric acid solution - the freezing point
36 ° but it up to 0 ° in completely discharge state, the electrolyte is water.