Battery power and capacity
http://www.cadex.com/b_08_0_cost.asp
           AAA Cell  AA Cell  C Cell   D Cell    9 Volt
Capacity   1100mAh   2500mAh  7100mAh  14300mAh  600mAh
Energy     1.4Wh     3Wh      9Wh      18Wh      4.2Wh