Always use a matched voltage charger and battery pack system. An undersized charger will never get the job done, no matter how long you let it run. Lead acid batteries should be brought up to full charge at the earliest opportunity. Avoid continuously operating batteries in a partially charged condition. This will shorten their life and reduce their capacity.
Inactivity can be extremely harmful to all lead acid batteries.
Store the battery in as cool a place as possible. 32 F. Batteries will discharge when stored, the lower the temperature the lower the self discharge. When not in use, boost every two months. Extreme temperatures can substantially affect battery performance and charging. Cold reduces battery capacity and retards charging.