HP Forums
Rebuilding a 21/25/25C battery pack - Printable Version

+- HP Forums (https://archived.hpcalc.org/museumforum)
+-- Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum-1.html)
+--- Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum-2.html)
+--- Thread: Rebuilding a 21/25/25C battery pack (/thread-99474.html)

Rebuilding a 21/25/25C battery pack - Bruce Bergman - 09-10-2006

Does anyone have a link or cheat-sheet for rebuilding a 21/25/25C battery pack? As far as I know, it uses two AA-sized 1.2V 250mAh batteries, correct?. I'm considering using 2100mAh or some higher capacity units, though. Any suggestions on where I can get a couple good Ni-MH batteries of this specification?

As far as removing the old batteries, it appears the backing plate on the battery pack comes off, but I'm too chicken to remove it without knowing how it's connected. ;-) Has anyone taken this apart?


Edited: 10 Sept 2006, 11:47 a.m.

Re: Rebuilding a 21/25/25C battery pack - hal - 09-10-2006

Hi Bruce,

I think you just slice it open with an exacto knife, and then glue it shut again. However, I would advise against doing it this way unless you have a means to charge the battry pack outside of the calculator (such as a woodstock reserve battery charger). There are numerous threads in this post advising against connecting woodstocks to the AC adapter (as the risk of overvoltage to the calculator is to great).

I re-celled the battery pack in my 29C by cutting out the center strip, enabling me to install and remove the cells easily so I can charge them in an external battery charger, not in the calculator.
Cell retention in the pack is not affected, and the missing center strip is not evident when the pack in the calculator.
There is a metal colnnector strip welded between the cells in the stock battery pack, which will go away if you do it this way, but this has not been problematic for me, as long as I keep the ends of the cells and the spring contacts polished (with an eraser).

I use Duracell NiMH 2500mAH rechargables, which really go a long time in my 29C.

Hope this helps, and best regards, Hal