Recommanded NiMh battery cells for HP82162A

[Hans Brueggemann]

(09-25-2017 03:26 AM)Neve Wrote:  Now, I have rebuilt the HP41 battery pack a coupe of days ago.
It was originally delivering 5.8v. Now it shows 4.94v. Even after 10h or so (I guess...) of charging it doesn’t go back up to 5.8v. Is this normal? I guess it would be since the original charger was not designed to charge Ni-Mh batteries.
...
On a side note, I also read that the charger is just a transformer. No electronics inside. The electronics inside the pack is what regulates the charging cycle. Do I understand this right?
If this is the case, can it be modified to charge faster and/or more efficiently? If so, how?

Thank you.

the internal charger electronics of the battery pack is basically a simple voltage regulator with resistive current limiting. hence, no real constant-current charging in here. it is that very voltage regulator that limits the fully charged voltage to what you did measure. and, yes, by limiting the voltage to a lesser than feasible level, the battery pack will never live up to what the batteries are capable of. that's a known given with this particular battery pack.

[rant on]
seems that hp got their good reputation (during the heydays of their pocket calculators, that is) by whatever product they manufactured, but for sure not from what they did in the range of battery charging. that area always seemed to be the demilitarized playground where they would unleash their cost-saving punks unto the designers.
[rant over]

so, yes, back to topic: if you know, what you are doing, then there is a slight room for improvement of charge current and end-of-charge voltage to adopt the battery pack to modern NiMH technology. is it worth the effort? depends on your personal use case. my use case is "infrequent use w/o card reader", which means that the battery pack dies ever so often by self-discharge, rather than real usage. so, my answer is no.