HP25 Replacement Batteriy Type

[Maximilian Hohmann]

Hello!

(11-20-2019 11:33 AM)Ignatz Wrote:  I also have a 3D-printed battery compartment on its way to me, so I won’t have to butcher the original...

What do you want to do with an original battery compartment that has corroded batteries in it? They will slowly "contaminte" everything else that is stored in the same box, like the proverbial bad apple... Eventually the old batteries will even swell and break their holder by themselves, I have seen that in differen calculators. So I think it is best to "butcher" the battery holder and get rid of the old (toxic!) NiCd batteries ASAP.

(11-20-2019 11:33 AM)Ignatz Wrote:  I’d want rechargeables, flat-top, but does the battery chemistry matter? NiMh, Li-on, NiCad?

Li-Ions are no good as they have the wrong voltage. You can either use NiCd or NiMh, they both work. Simple ordinary cells from the supermarket (they sometimes have rechargeable batteries in my part of the world) or electronic store. Personally I would stay away from NiCd because they contain very toxic Cadmium. Also, NiMH cells have a larger capacity. 2000 or 2500mAh work fine.

Regarding the charger: As already written in 100+ threads here, make a habit of not pluging that charger into the calculator. Ever. The biggest part of the Woodstock series calculators were (and are!) killed by their own chargers. Charge your batteries in a standard external charger instead. Since they have five times the capacity of the originals (which were 500mAh NiCd cells) the original charger is too "weak" for charging them anyway. Especially NiCd cells suffer from low current charging and can lose part of their capacity in the process ("memory effect"). This does not apply to NiMh cells, so another reason to use those!

Regards
Max