battery holder for HP 41C


My HP 41C is dead. I think that my NiCd-package gave up working. Since I do not find my original battery holder for my calculator I am not able to use my HP 41 C any more.
Does anybody know where I can get a battery holder for my HP 41C ?



I heard that you can find it in CALPRO.

Here is the e-mail


Here is a perfect chance to fix something!

The HP41 nicad pack isn't the easiest to open, but isn't too hard either.

Replacement cells are fairly easy to come by, and depending on how handy you are with a soldering iron (you'll need one) you can also modify the charging circuit to prevent nasty surprises later.

I'll have to drag up the circuit diagrams and take some photos to make an article on it...


When you have a better charging circuit, I'd really like to see it. I could design one by myself, but everything I design ends up with containing at least one microprocessor + 15 supporting chips :-)

I have then to minimize it and produce my own chip for these limited space purposes :-)

If you post it fast, I could integrate it into Christians battery pack.


It's in the email...

Nothing with more than 3 leads!!!!


Steve, what size battery do you use? Can you get the 1/2N in Australia?


I bought a couple of packs of 1/2 N from the US a while ago (in advance of getting a nicad pack of my own to fix) but for other packs that I've fixed, I've used 1/3 AAA


Erik, I recently (within the past year) had two 41c nicad packs rebuilt by a company called Powercell Repackers here in Australia (~$US20 each). They used N75, not 1/2AA or 1/3 AA, I am pretty sure N75 are the correct cells, and I checked that they could source these cells before I went ahead with the job. I can give you some contcat detailes if you're interested. Cheers, John


Hi John, I just rebuilt one with 1/2 AA. Talk about a tight fit! The good thing is they have higher capacity than the 1/3 AAA or 1/2 N. Are N75 a metric type size? I will have to see if I can find them here in the US.


I believe the reference was to Sanyo Cadnica N75P 1/3-N size cells. HP 41c packs I think had 1/2-N cells, didn't they?, but since those had all disappeared, the 1/3-N's were the next best thing.

But even the 1/3-N is dying. Sanyo is/was the last manufacturer supplying "N"-dimensioned NiCd product in the U.S., and a survey of their website seems to indicate that they have dropped all "N" diameters in favor of AA and AAA.

Some spot supplies of the N75P cell may still be around. I bought 16 recently at a Batteries Plus, and had them spot weld tabs on each (I already have a project for them, sorry). Since there are some 170 Batteries Plus stores in the U.S., it might well be worth a sweep in YOUR area.

And as Katie Wasserman has pointed out in her excellent summary (Articles Forum), 1/3-AAA NiCads are smaller and so will fit great. Their capacity, while not as large as the N75P, is probably very much in line with the old 1/2-N NiCd cells that were manufactured 25 or more years ago...

By the way-- other configurations of batteries may prove entertaining, if you're a designer-type. Varta makes button-cell NiCds; paralleling a couple of these to increase capacity and so forth, you might come up with an optimal packing of that plastic shell... :-)


I made a mistake in my earlier post. I used 1/3 AA NiCads. To get these to fit, I had to mill out the inside of the plastic case, amongst other things. The great thing about using these batteries is they provide 110 mAh each for a total 440 mAh. This is more than twice the capacity of the 1/3 AAA. The big negative is it was a very difficult rebuild.


> they provide 110 mAh each for a total 440 mAh

Erik, since the cells are connected in series, you'd still only get 110 mAh; but you get that 110 mAh at the nominal voltage of 5V instead of 1.25V.



Hi Christian

Since you live (or at least work in Vienna - University of Vienna) we could meet and rebuild the battery pack. It's not that hard, if we try to get the next matching batteries. The originals are not available anymore, so we'll have to replace them with another type.

I'm working in the TU Wien (University of Technology, Vienna) and you can reach me (Wed-Fr) using this phone number 58801/42811 .

It's an easy fix, as soon as we have the accus I think it is done in minutes. I'll try to find out where to get them fast. I would have answered in German, but don't consider this being polite in an English message board.

If you send me an email (, checked three or 4 times everyday) you can get my mobile number too.

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