Batteries are a perishable product and start deteriorating right from the time they leave the manufacturing plant. Although the degradation rates are lower for some systems, it is not advised to store batteries for a long period of time prior to use.
All batteries should be kept in cool and dry storage. Refrigerators as a storage media are recommended, but freezers should be avoided because not all chemistries are suited for storage in freezing temperatures. When refrigerated, the battery should be placed in a plastic bag to protect against condensation.
The NiCd battery can be stored unattended for up to five years. For best results, a NiCd should be fully charged, then discharged to zero and shorted at the terminals. If this procedure is impractical, a discharge to one volt per cell and storage in a cool, dry place is acceptable. A NiCd that is allowed to self-discharge is subject to formation of large crystals (memory).
Prolonged storage of NiCd (and NiMH) requires priming the batteries before use by applying a slow charge followed by one or several discharge/charge cycles. Depending on the length and temperature of storage, two to five cycles may be required to regain full performance. The warmer the storage temperature, the more cycles are needed. Some cycling may be required after as little as two months of storage.
The SLA battery can be stored for up to two years but must always be kept in a charged condition. Periodic topping charge is required to prevent the open cell voltage from dropping below 2.00 volts. (Depending on the manufacturer, some SLA batteries may be allowed to drop to lower voltage levels). If permitted to self-discharge below that critical voltage threshold, sulfation occurs on most SLA batteries and the recharge characteristics change, possibly affecting cycle life. Although the capacity of the cell can mostly be restored by cycling, it is desirable to recharge the battery before the open cell voltage drops below 2.10 volts.
Similar to the SLA, the Li-ion must be stored in a charged condition. If stored below 2.5V for a period of three months or longer, unrecoverable capacity loss occurs. Corrosion from leaking cells may also occur. Some Li-ion batteries prevent a recharge if the cell voltage has dropped below a critical level. This is done for safety reasons, because a cell that has been discharged too low has chemically been altered and a recharge my be hazardous. Best results are achieved by storing the Li-ion battery at 70 to 90% capacity level. Some manufacturers may recommend lower storage capacities.