An ALKALINE 9v "transistor" battery (PP3 etc) has a capacity of
    around 500 mAH.
        :
    Here are a few TYPICAL capacities for modernish batteries.
    All these are in milliamp  hours.

    Alkaline    AA          500
    NiCd AA                 500

Those don't corrolate.  A typical 9V alkaline battery contains 6 AAAA
cells, so would of necessity have a much lower mAH rating than an AA.
Also, a NiCd usually has significantly less energy than an alkaline
(although a higher current capability) (as with the C/D cell numbers.)
I therefore think that the quoted Alkaline AA capacity is incorrect.


    NiCd C                1800
    NiCd D                 4000

Another thing to watch out for is that many of the "consumer" D cells
are actually C cells in a bigger package (keeps prices lower.)

IIRC, the duracell web site includes a fair amount of technical
information, including the discharge curves for their common batteries.

BillW