HP Classic Models Battery Pack Rebuild


I hope someone will have the knowledge and experience to assist me regarding HP-35/45/55/65/67/70/80 rebuid battery pack:-
(1) I used the recovered battery pack holder and metal strips and rebuid 2 battery packs using the same type of batteries (NiMh).
(2) After the rebuit, I tested both with digital multimeter and confirm that current are in fact flowing through each pack's metal strips because each pack registered approximate 4.0 volt (freshly charged).
(3) However, and this is the strange thing, one of the pack is working perfectly when I put it into the calculator and the other just failed to light-up the display of the same calculator. I've checked many times and confirm that the metal strips are in fact touching the calculator's contacts, but yet nothing happen!
4) Can someone throw me some light as to how to go about diagnose this?
Your valuable comment is very much appreciated.


I assume the failing battery pack contains a bad cell.
Please measure the voltage across both battery packs
unloaded and loaded with a resistor of about 100 Ohm.
If one or more cells are broken, the voltage will drop
significant compared to the unloaded value.


Clear very well the metal strips on the battery packs.

Edited: 18 Feb 2011, 12:42 p.m.


A couple of unlikely possibilities:

When you probe the battery pack, could the pressure of the probes be making the metal strips contact the cells in a way that isn't the case when the pack is tried in a calculator?

Are the cells installed with the right polarity?


I recently rebatteried my cell phone. I use eneloop ells which are the best at charge retention. I have put my old Nimh cells ready for proper recycle as provided by San Diego city. Sam


Are you sure your system is charging the batteries?

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