From Nikon
EN-EL3e Li-ion Rechargeable Battery for Nikon digital SLR cameras. Keeping a spare battery on hand ensures that you will always be ready to capture the images you want most. And, while Li-ion rechargeable batteries are less prone to recharge "memory," using the normal complete charge of one battery before recharging will better ensure optimum rechargeable battery life. A freshly charged spare battery allows this and provides uninterrupted photography.
After reading varius reviews on how the off-brand batteries may or may not work, I decided to get the original Nikon battery for my D80. I got it at a good priceof $37 before Christmas. I am happy with it. I get quite a few shots before I have to put the other one on. Obviously, you can tell that I have two and this helps out a lot in that I have one ready when the first one runs out.