dave - i (for school project) am making a portable pre-amp, and wanted an extended capacity, and rechargable, so i have a battery for you to check out....
these are Nickel Metal Hydride, rechargable, good batts.
the 9V PP3 type are about 150mAh where as the ones i found called 2/3AA are 700mAh AAA are 750mAh and AA are around 2000mAh. the 2/3 AA batts have the same diameter as the AA but are shorter, and more compact, so check these!
cya
mike