This from Wikipedia...
"""Battery Storage
Batteries should be monitored and periodically charged if in storage, to retain their capacity. Batteries intended to be stored should be fully charged, cleaned of corrosion deposits, and left in a cool dry environment. High temperatures increase the self discharge rate and plate corrosion. Lead-acid batteries must always be kept in a fully charged condition. the terminal voltage can be measured as an indication of state of charge. Batteries may be charged periodically by a constant voltage method, or attached to a "float" charger."""
More under the heading Car Battery & Lead Acid Battery
Peccavi
September 2009