Thanks I'll look deeper into these.
After almost exactly 2 years of pretty constant use, my 9.6V Maha Powerex batteries are now failing and must be replaced, either with new ones or something else.
BTW, the Maha 9.6V charger for these runs off 12VDC, and can be fed by any wall wart, cig-lighter adaptor, or whatever, that outputs 12VDC (with enough current and the right plug of course). That was a big factor for me. I think the wall wart that came with mine from Thomas Distributing works on either 110 or 220VAC and was only like $3 more but I'd need to confirm that.