Differences
The battery packs are quite similar. The D70 camera has an EN-EL3 rechargeable lithium-ion battery. The D80 camera has an EN-EL3e rechargeable lithium-ion battery.
Compatibility Between D70 and D80 Cameras
The 'e' on the end of EN-EL3e stands for the electronic battery monitor chip inside the battery. This EN-EL3e battery that comes with the D80 camera will work in the D70 camera. However, the EN-EL3 battery that comes with the D70 camera will not work in the D80 camera.
Compatibility With Other Cameras
The D80 battery pack also works in the Nikon D50, D70, D70S, D80, D90, D200, D300, D300s and D700 cameras (see reference 1.) The D70 battery pack also works in the D100 camera.
Battery Life
One of the major differences between the D70 and D80 cameras is their battery life. The battery life of the D70 is around 1,000 shots, whereas the battery life of the D80 is between 1,000 and 2,000 shots.