Maybe this will help out some:
The average 9v alkaline battery has a capacity of around 350mah useable power at a low discharge rate.
The average 9.6v rechargeable NiMh battery used as a replacement for standard 9v batteries has a rating around 250-300mah at medium to low discharge. I've charged them from and gotten results from 100mah to over 500, sometimes you get better cells.
The average AA alkaline battery has a capacity of around 1500mah of useable power.
The average rechargeable AA NiMh is around 2500mah.
Whoa, big difference. What gives? Well, the size. A 9 volt battery is actually a series of six 1.5v cells. This means that they have to fit six cells in that small 9v package. Obviously the cells are going to be tiny with a low energy capacity. One AA battery is only one 1.5v cell. That cell is about 8 times the size of one of the 9v battery's cell. So it has 8 time the capacity.
Long into short, this is the easiest way to understand it:
Two 9v batteries in parallel = 700mah
Six AA batteries in series = 1500+mah
So you get twice the useable power at the same voltage using six AAs instead of two 9v batteries.
Last edited by Tempted : 10-09-2012 at 06:12 PM.