Converting HP-25 to NiMH batteries, possible?

[cubytus]

Wow, I never expected such a quick response! Thanks all!

Well, since this HP-25 is not the "continuous memory" version, swapping the batteries would result in any program being erased. No big deal, but worth mentioning. No need for "flat-top" versions as these seem even harder to find than NiCd, plus they wouldn't fit a standard NiMH charger. I used a battery contact spring to close the circuit in the battery box, but was surprised to see the calculator contacts weren't spring-based back then.

In the meantime, I read that NiCd and NiMH don't have the same charging profile, and that NiCd, while being lower capacity, are far more tolerant of overcharging, and this is precisely why the charging circuit uses it as a voltage regulator.

So I understand that no-one attempted to convert the on-board charging circuit to NiMH?