When you buy rechargeable batteries like the EN-EL2, or get some with your
camera, make sure you read the instructions that came with them. The
most critical issue is whether there is some conditioning you should
do when you first get them. For example, we've seen instructions to
charge your batteries before you use them the first time, give them
a chance to cool down, then charge them again, give them a chance to
cool down again, and then charge them again.
When you recharge your battery you're using up a recharge cycle, and coming
one cycle closer to not being able to recharge anymore. Lithium ion
and lithium polymer batteries need very different treatment, and
often come with instructions to charge the battery every chance you
get. With no memory effect, there's no need to run the batteries
down, ever. Keep in mind, however, that the best way to maximize
battery life varies even from one battery model to another. The rule
remains: read the directions that came with the batteries.