According to Energizer's website, their batts are rated as follows - first plain old Energizer, then E2 batts:
Batt | E mAH | E2 mAH
-------------------------
D | 18,000 | 18,900
C | 8,350 | 9,185
AA | 2,850 | 3,135
However, this doesn't tell the whole story. IME, alkalines just plain don't last as long as NiMH rechargables. Apparently, NiMH batts do better than alkalines when taxed by higher discharge rates, something to do with the different chemical makeup. What exactly, dunno!