iFixit

Lifting off the LCD exposes the iPad 2's battery; A 3.8V, 25 Watt-hour unit. That's just a hair more than the original iPad's 24.8 Watt-hours, so any improved battery performance can be attributed to software and other hardware improvements.

Also listed on the battery is a capacity of 6930 mAh, which may appear to contradict the already mentioned 25Wh at 3.8V ((25Wh/3.8V)*1000=6579 mAh), but 3.8V is the listed nominal voltage, not the average voltage. The average voltage of the battery over a full charge/discharge is closer to 3.6V leading to a more accurate calculation ((25Wh/3.6V)*1000=6944 mAh).

After disconnecting its cable, the display can be removed from the iPad 2.