BCTweaker said:
A good reason is because a 9V can't source as much current as even a single
AA cell for the same duration due to their much smaller individual cells.
There are six seperate 1.5V cells connected in series to produce the 9
volts. The cells internal electrodes have significantly less surface area to
interact with a much reduced quantity of electrolyte. If you still need 9
volts for a circuit try ganging six AA's in series. If weight is a concern,
even AAA cells aranged in a battery of 9 volts will outlast most 9V's.
Of course, since all of your above comments still apply.
Now try ganging 6 alkaline watch batteries together instead.
There is no mystery here. If one uses exactly the same battery technology in
each case, the larger battery will have more storage capacity.
(packaging excepted of course, and in the case of six separate cells, this
will usually increase)
So the answer may be to use a larger 9V battery. Unfortunately these aren't
common any more. Most people prefer to use the smaller size, and change it
more often.
MrT.