How to store a rechargeable batteries
Different kind of rechargeable battery chemistry requires different kind of storage procedures so that the batteries do not get damaged when they are stored.
In case of NiCD rechargeable batteries it’s advisable to discharge them completely if you want to store them, the quickest way to damage a NiCD batteries is by leaving them on a charger for extended periods of time (being topped) or storing them in a charged state.
In the case of NiMH batteries the best way to store them its to partially charge them around 30 – 35% before storing them, then use a charge / discharge cycle on then every 3 months to keep the batteries vibrant, also its a very bad idea to keep NiMH rechargeable batteries plugged on a charger for extended periods even if your charger has a trickle charge mode, as extended amount of trickle charger for days / weeks will damage a NiMH battery and thus reduce its serviceable life considerably, this is even more important for LSD NiMH batteries.
Remember if you store NiCD and NiMH rechargeable batteries for extended periods of time these batteries will take a couple of recharge cycles (3 – 4) before they regain their full capacity, a conditioning cycle is a good idea after extended storage.
It is also important to store batteries in a cool and dry environment a temperature around 20 degrees Centigrade is ideal, some people also store batteries in an refrigerator its not necessary but if do that make sure you seal them in a zip lock so they are dry and no moisture is present and before charging the battery let it come to room temperature before charging.
For Li-ion batteries its best to charge them around 40% before storing them, also Li-ion batteries lose very little charge while they are stored.