"memory" is only really a problem with the niCads. NiMH (nickel metal hydride),Lithium Ion, and lithium polymer batteries don't really suffer from "memory" any more.

Store NiCads and NiMH fully charged, in a FREEZER. That's right. At room temperature (about 70 degrees) NiCads and NiMH will lose several percent of their charge PER DAY. If you charge them up and stick them in a freezer they'll hold 90% for a month or more. Best to bring them up to room temperature before putting them back in service.

I don't really use lithium ions any more, but they are a lot like lithium polymer batteries in how they are treated. Long term storage at between 50 and 85 degrees with battery at 40% charge.

I had to learn a LOT about batteries. I fly RC aircraft on electric motors. Motors are HARD on batteries and the lithium polymer batteries (preferred for the planes) are expensive. So we try to get the best performance and life that we can from them. Most guys get 2 to 3 hours of constant use out of their radios (with the factory battery). I get 10 hours minimum (I hot rodded the battery pack... pulled out the factory one for a custom pack I ordered)... just a little explanation of how I got "battery smart" :)