Hello Tom

Although I can not answer your situation directly, I have experienced this with the 7.2V racing batteries of NiMH type. The issue that may be causing this is a false peak charge that the charger is stopping before it is fully charged. For NiMH batteries there are two such peaks to overcome. One is detected by the negative delta method and the second by another means that I can not recall at the moment. Once I replaced my charger with a new one the problem of partial capacity charging went away.

Also as a note, some of the chargers are not designed for smaller mah batteries as these are generally charged at a lower current rate. Quick charging a small mah battery may cause damage. Also the charging characteristics for the smaller mah battery may trip the charger into believing the peak has been obtained.

If you can 'hard charge' the battery with a dumb charger (without automatic electronic control) this may alleviate the problem, or at least verify if the charger settings need adjustment for this type battery.

Cheers
Eric Scott