CAP matching does sound like a problem, perhaps it would not be that bad, it would be an expensive test to find out however.

The computer can compensate for reduced capacity as the batteries age, and it will recalibrate when a new battery pack is installed (people have reported this) so it seems likely that it could compensate for a larger battery pack.

Good to know they are D-Cells anyway.

We shall see if in a few years I am adventurous enough to try it. :-)

Note: CAP matching is simply a charge/discharge test, they measure how much the battery holds. I don't know what normal variation is, nor how much tighter the HCH's requirements are. You can do it yourself with a stopwatch and a discharge circuit. You need a highly accurate charger (they are not that expensive), or you could make do with a trickle charger and let it overcharge slightly. Hard to imagine doing this test by hand with 120+ cells.