NiMh 'N' Batteries for the HP-41 Calculator in UK


If anyone is looking for rechargeable NiMh 'N' batteries for the HP-41 calculator in the UK, they might like to note the following two sources:

with a search on 'GP36NH'. Another source for the same battery is:

They cost about £1.80 each.

Sadly I have not yet found a source for the 1/2 N GP18NH for use in the rechargeable battery pack (even though GP Batteries lists them as available).

Brian Gladman


I have found a very good replacement made with a 1/3AAA NiMH cell (150mAh) which has the same length as the 1/2N but diameter is 10mm instead of 12mm. But I have found a tube that compensates the outer diameter. So you get 1/2N sized cells.

I am offering these in the ademertisemnt section but I can send information to anybody interested on doing it by himself


Here we go again.

Unless you want to spend a lot of time using the card reader, the
consensus is that its better to use alkaline batteries with the 41C. Rechargeable batteries are a lot of pain for this machine:

a) even when fully charged they are close to the LOW BAT warning level

b) they lose their charge faster than alkalines, meaning that you have to deal with them far more frequently than with alkaline batteries.

c) I have found that the smaller the form factor the more likely the battery will leak or outgas. (Notice that HP-97 calculators are far less likely to be suffering from corrosion than the HP-67)

d) Back in the early 80s N-size alkalines cost a lot of money, today they are cheap enough that most people can afford to replace them once a year or so.

NiMH cells are great, I use them in all sorts of electronic equipment, its just that they are not really suitable for this particular piece of equipment.



Hi all.

Hi Vassilis.

For what it's worth, will the posters PLEASE listen to this man.
Like myself, he is practical and knows what he is talking about...


Anyone who wants to run rechargeables in his 41 HAS ROCKS IN THEIR HEAD. YOU WILL GET IRREVERSIBLE CORROSION PROBLEMS, particularly if you have a CX.

Don Wallace


Vassilias said it best, here we go again.

Anyone who wants to run rechargeables in his 41 HAS ROCKS IN THEIR HEAD. YOU WILL GET IRREVERSIBLE CORROSION PROBLEMS, particularly if you have a CX.

So a CX is different with respect to battery corrosion? This is absolute nonsense. So the operating current is a bit higher. Big deal, so what? So the standby current might be higher, big deal, so what? You're still talking microamps.

Irreversible corrosion problems? Absolute nonsense. Alkalines destroy 41's when they leak, rechargeable out gassing and the resultant minor corrosion cleans up fine. I'd rather clean up a 41 that had an original 82120A left in it for ten years untouched than a 41 with N alkalines or worse yet old carbon zinc cells.

It is dead easy to rebuild 82120's with modern 1/3AAA nimh cells. They work fine, that's been documented here for several years. If people want to rebuild their rechargables, let them. If people want to use alkalines, let them.

Don, why do you have to shout at people and tell them they have rocks in their heads? Be civil, be informative. You're just being rude and helping no one.

Edited: 21 Oct 2005, 10:29 a.m.


I have measure the "OFF" current of many HP41 calculators. 41CX machines are no different than the others. Yes, they have a clock in them that draws current but the chips in them are built on later technology and tend to draw less currrent. On the whole the standby current is the same for a 41C, CV, or CX. The batteries cannot tell the difference... unless they can read the label on the machine.

A VERY good reason to rebuild the rechargeable pack is because it is all that you have. Many machines no longer have their "N" cell holders. Also a lot of people do use the readers or HP-IL constantly.

That said, use "N" cells if you can. No need to worry about self discharge.


This Message was deleted. This empty message preserves the threading when a post with followup(s) is deleted. If all followups have been removed, the original poster may delete this post again to make this placeholder disappear.


Excerpts from Don's post:


The posters here who are experienced are readily differentiated from the "hacks" and hobbyists (who are all fine people btw).

Where certain parts of this forum get (imho) quite bizarre at times is where people who do not know what they are talking about berate people who actually DO. There is no need for it.


I have met some really remarkable people here. Maybe you are one too. So far, in your replies, I haven't seen it. Am I missing something? (I doubt it...)


If that person wants to ignore me or pick me up on real errors then thats fine. Try as I might I can't find a (rational) reason why you insist on abusing me for helping someone else. If you disagree, then that's fine (even if you are in fact wrong!) But the only person in this thread who is being abusive is you, sir. And for NO GOOD REASON.


By the way, I do not care if you are a qualified engineer or an experienced tech. But it does not sound that way to me. You don't seem to be in any way practical.

I suggest: Get some experience with this hardware, real batteries and respective flaws and faults, then come back and abuse me if you want to further sully the forum. In that case, back up your comments with provable FACTS, please.


I try to help people here from a position of very SOUND EXPERIENCE backed by SCIENCE. I DO NOT go off half cocked or abuse / berate people. Please guys, do us all a big favour and kindly follow Vassilis lead if not my own and DO THE SAME. Show us that common courtesy at least.


In closing I want to apologise to Dave Hicks for drawing yet more "heat" from a person who may want to rag me rather than help the poster. ... Abrasive cirticism is not warranted in a forum of this generally high quality. I personally couldn't care less at being criticised (by amateurs?) but find I feel acutely embarrassed for the other readers. Sorry to you all, (except my misguided critics).

Wow, that's a lot of petulant, indignant piffle.

FYI: Randy Sloyer has plenty of sound practical experience, and has posted here regularly for at least several years. He has repaired several of my fullnut 41's that arrived "alive" but malfunctioning, and returned them to me in perfect working order. He knows what he's doing, and knows how to fix other models as well.

You can find Randy at

About the battery issue: I would tend to believe Randy (on limited evidence, admittedly) that leaking alkalines will permanently damage the battery contacts, while a leaking NiCd might not.

I've seen damaged HP-41 battery terminals (of which I'd surmise most ran on disposables, once they became available and economical). However, I've seen no terminal corrosion on any of my the three HP-34C's, even though rechargables had been used on all of them at least for a while, and I received sets of dead, "fuzzy" NiCd's with two of them.

-- KS


This Message was deleted. This empty message preserves the threading when a post with followup(s) is deleted. If all followups have been removed, the original poster may delete this post again to make this placeholder disappear.



I normally try to stay out of this kind of discussion, but what the heck.

I am not on any horse, Karl... I get annoyed when I am abused publicly.

Now I understand WHY I drew some flak from Randy et. al. People don't like competition...

Aren't people interesting. I never cared for politics.

I am still happy to participate here, but I won't cop abuse; it is as simple as that.

Perhaps I'm missing something, but I can't see where anyone is really abusing you? Yet in this last post, you seem to be implying that the people disagreeing with you on technical points are only doing so to 'profit from the forum'. Is that correct?

For the record I agree with Karl.

Rather then question Randy's credentials, how about we keep the debate purely on technical terms. I do not believe there is a conspiracy to pass bad technical advice for profit.

Please note that I have zero financial interest in this forum. I have never had anything to do with Randy so there is no conflict of interest.



Edited: 25 Oct 2005, 9:55 a.m.


Quo usque tandem abutere, Catilina, patientia nostra?


Usque ad nauseam!!


Edited: 26 Oct 2005, 7:26 a.m. after one or more responses were posted


So you speak Latin... Big Deal.

Please repeat your comment in english so it's in the open.




What is the point in your speaking Italian?

Please repeat your comment in English, so it's in the open...




What is the point in your speaking Italian?

Ahem, that's latin, indeed.

I thought it was known enough to need no translation but... since you ask:

For how much longer, Catilina, will you abuse our patience?

Marcus Tullius Cicero (January 3, 106 BC – December 7, 43 BC)

o tempora, o mores...


--------------------------------------------------------------------What is the point in your speaking Italian?
Ahem, that's latin, indeed.
I thought it was known enough to need no translation but... since you ask:

For how much longer, Catilina, will you abuse our patience?

Marcus Tullius Cicero (January 3, 106 BC – December 7, 43 BC)

o tempora, o mores...

Thanks for translating.

No shame in me not knowing latin. It's only "Old Italian" ;-)
I choose to ignore your put-down. Do you like hiking?

Cicero is cool. I prefer Chomsky. He is more current and pertinent.

You guys are NOT the ones whose patience is being abused...
I can assure you it's the other way round.

Anyone with a problematic 41 who wants to speak with me privately can do so. I will not bother to help anyone publicly here anymore.

No-one has backed up any criticism of my posts with solid technical fact.

I apologise for some inaccuracies in my posts. None of them are technical ones.

It's been great, I've met some interesting and pleasant people.
Now I am going to leave you all to your "game"...

Tony and Randy (and Jon) are obviously now happy.
Nice MO you have there, guys.



Oh for crying out loud, Don! This is the third time I know of in the last couple of months you have flounced out of here forever, only to show up again in a day or two. Grow up, why don't you?

And you might try sitting on your hands a little bit when you feel like making an angry retort. It could save you embarassment of the type you incurred in this thread.

Friendly advice, believe it or not.


I believe the translation is not very accurate. However providing a good translation might not be welcome by the forum moderator...



Hi Arnaud,

You're right and I'll exercise self-censorship by deleting the non-proverbial part of my post.

Merci et cordialement.


Edited: 26 Oct 2005, 7:27 a.m.


Te futueo et caballum tuum!

In future keep your comments on topic please.



Please note that Don Wallace is a self-described *Asperger's* sufferer.

Please note that this syndrome can make a person appear to be highly anti-social and abrasive.

It may be best to simply ignore his annoying comments but respond only to the relevant on topic information.

Common issues with Asperger's (not all are necessarily present):

--no friends in school years;
- lack of physical coordination;
- unable to hold a conversation outside of a limited subject matter;
-**NOTE** Easy to provoke and often lashes out with excessive force or violence;
-often attempt to dominate social situations;
-often test at genius level for math;
-difficulty smiling;
-strange sense of humor, taking all statements literally--difficulty with irony and nuance;
So, bear these facts in mind. To keep it civil around here, we need to understand each other :-)

Edited: 26 Oct 2005, 9:46 a.m.



Thanks for your post.

Actually, very few aspergers people are violent. The other points are or "appear to be" pretty accurate. For violence / callous disregard for others welfare you can't go past either pychopaths or politicians. (Think about it...)

We don't set out to dominate social situations, we just lack the subtle devious character of the average human being. Others see we are different and subconsciously resent us. Very strange dynamic that leads to "AS" sufferers being bullied. Their resulting anger can then spiral a bit. We don't like B.S. either and can smell it a mile away!

We "A.S." people have MANY really good features too, such as amazing attention to detail, reliability in relationships and friendships, an extreme degree of honesty, loyalty, reliability at work and a very strong sense of fair play. A very unusual and valuable group of totally misunderstood people often operating at a genius or for a few supergenius level of intellect in NARROW areas. Socially, we are a bit of a TRAINWRECK. Oh well, can't have everything...

We are also very unusual in our total disinterest in social "norms", political behaviour and are disinterested in manipulating others. We cannot read body language, miss social cues and have trouble with verbal sub-text sometimes. This makes us easy prey to setups and manipulation by others.

Once a sufferer learns to live with it, they can learn to behave "normally", much as a child might learn the piano, through a large amount of study and work. I had to actually study body language out of books and then study "live" subjects ;-); now I can read it like a pro and I'm doing it CONSCIOUSLY (hard work!).

Given how "normal" people behave, I would rather be an Aspergers "sufferer", but it's a hard life for many.

I value the people in this forum highly enough to come clean about my "affliction".

We also make GREAT engineers!

All the best, everyone.



Given how "normal" people behave, I would rather be an Aspergers "sufferer"

With all respect, but what's wrong with normal people behavior?


I've read that some "medical archaeologists" think that, among
other famous people, Thomas Edison and Albert Einstein may well
have been Asperger's syndrome people.

Well, it seems that Edison didn't always "play fair", but he
certainly made a difference.

But let's keep in mind that Asperger's covers a wide range of
traits, and those who have it should be treated as individuals.
For some notes on Asperger's see

For what it's worth, a student nurse reading about Asperger's told
me that she thought it described most of the men she knew.

Written language has subtle nuances that are easily missed,
particularly in an international setting such as this, where
different dialects of English are used, and for some, English is a
second language. A reader should try to "read between the lines",
particularly when what he's read seems unreasonable or rude. A
good (but probably unobtainable) goal for a writer is to write in
a manner that not only can be understood, but can't be

Don, in your case, knowing that you have this condition, perhaps
you should make special efforts to avoid being overly sensitive to
criticism or seeming rude when you don't really want to be.
Practice your empathy; that is, always try to imagine how the
other person feels. Maybe write whatever you intend to post in a
text file, then save it, take a break, and reread it carefully
before pasting it into the Forum's text box, and even then,
"preview" it before actually posting. Once posted on the Internet,
it can never be totally withdrawn, even if the post is deleted.




Don, in your case, knowing that you have this condition, perhaps
you should make special efforts to avoid being overly sensitive to
criticism or seeming rude when you don't really want to be.

Perhaps easier said than done, of course. I would also rate it as particularly difficult in forum with lots of other prickly egos and polyglot confusion.

Naturally, I'm referring to a hypothetical forum. 8)


Yes, no doubt easier said than done. Still, all of us who participate should make an effort to get along with everyone.



We've seen our fair shair of misunderstandings here--far fewer than om many frums. We've had pretty good success over the past 2+ years I've been here, mending fences etc. There have even been misunderstandings between some keystone members--and we've all learned from it and gotten along.

I will stay confident that we will, once again, all learn from each other and continue this wonderful virtual universe of ours.

Thanks to dave too--the structure and the organizationof this place influences the spirit.




I agree that it makes little sense to bother about rechargeables unless a lot of use is being made of the card reader.
But in my case I do use the card reader very extensively so NiMh cells make sense.
I don't yet have the evidence to comment on longer term issues with corrosion but I have not found any problems with low battery warnings since the GP36NH N cells I found are providing for extensive use of the card reader without any early 'low battery' warnings.

Brian Gladman


Hi Brian,

Thanks for the feedback. I love NiMH cells. They are a different kettle of fish to nicads.



Hi Don,

I am pretty happy with the GP36NH cells so far but I will be keeping a watch for any corrosion issues.
The big problem with these cells is that pretty well all commercial chargers are not designed to cope with cells with such small capacities and charging currents. In consequence it is very easy to overcharge these cells and hence break their seals.
To overcome this problem I am using a charging method that allows both cell temperature and cell delta-V to be constantly monitored so that charging can be stopped immediately full capacity is reached irrespective of the initial charge state.

Brian Gladman


Hi Brian,

Yeah, very cool.

I am certain that your finding will be very interesting to
everybody here who owns and runs a 41. They are a great old calc.
I for one really appreciate your great feedback.



Who is this Donald Wallace?
May be an engineer from HP calcs division?
Just curious:-)).


Hi Jon! Hw are you?

How's YOUR repair business going?...

OF COURSE I am not an hp engineer. ;-)
What's your story?


Edited: 25 Oct 2005, 5:14 p.m.


Hi Don:

Fine, thanks for the interest.
I see that you are not so rude now.

In case you have something to repair or need some information to do it yourself just contact me back.

In my opinion you should send to me your HP-41CV (the one that I can see in your webb). Don´t feel ofended, but your repair is too agresive and not the best option for that model.

Congratulations again for your new attitude



Hi Jon,

My old 41s are both fine thankyou. Why would I send you something I repaired? Certainly there is nothing wrong with the repair. It works and is solid. Your opinion, though in itself valued, is not valid.

I think you have a good sense of humour. Certainly an asset.

I decided to stay here for now as people may need some protection from the BAD ADVICE of a few others... I am happy to fill that role.
That would mean maybe I should be more critical? Certainly don't need to get abusive. In any event there is no payoff for me, but a few people with problems will definitely benefit.

No offence meant, but I would be happy to put my ([fine or motor] mechanical or [signal or power]electronics) repair skills against yours, Tony D.'s and Randys any day of the week. I see many errors in the advice these two gents give but I have the coutesy to avoid criticising them. That courtesy is not reciprocated and given their personalities and motives I don't expect it.

To the guy who speaks in latin: of your comments I ask:

Que bono? {you can correct my spelling ;-}

To date no-one in the forum has offered any concrete refutation of my two statements of damage from nicad cells/packs or wrecking displays by disassembly. Some have offered concrete info which in general supports my assertions. Therefore my judgement and advice in this matter is sound. More important, my motives were good.

In future I will not respond to criticism because all the other people who jump on the bandwagon obviously do not know what is really going on and their comments (if on topic) are not technically relevant or accurate. No offence meant.

I HAVE managed to bootstrap a small repair business for people down here in OZ and for that I am grateful to the forum, to Dave Hicks for hosting us all and to the unnamed software wizard who directed me here in the first place as he thought people here might benefit from my experiences. He doesn't post here anymore btw and given the behaviour of people here I do not wonder why. He's not the only one, either.

Thankyou to the people who have written to me expressing support. A few of you are leaders in your field. It's fun to push that envelope!

To you Tony and Randy I wish you every success in your business / work endeavours. To everyone else, good luck with your d-i-y repairs, may all your problems be little ones, long live hp hardware and roll on BUG SQUASHING in the various add-ons people have devised. I haven't seen any bug reports yet...(nor likely to?). The people I refer to know who they are.


Edited: 26 Oct 2005, 6:50 p.m.


Hello Don,

I decided to stay here for now as people may need some protection from the BAD ADVICE of a few others... I am happy to fill that role.

You have now announced that you are 'leaving forever' at least three times now, only to come back within a day or two. Either stay or go, but please make up your mind.

This 'debate' keeps coming back to one issue: You claim others are giving bad technical advice. You have implied multiple times that other regulars on this forum are either incompetent, motivated by greed, or both. You have also stated that others are abusing you purely because you corrected their bad technical advice.

I am having a great deal of trouble finding evidence to support this. You have a habit of deleting your comments. I have searched virtually every message on this forum in the last week and cannot find any message where someone even mildly abused you, where you didn't ask for it first. Someone asked for you evidence of where you were abused, you declined.

From what I've seen, you've constantly insulted people, although subtly. To take the root of this thread as an example

Anyone who wants to run rechargeables in his 41 HAS ROCKS IN THEIR HEAD. YOU WILL GET IRREVERSIBLE CORROSION PROBLEMS, particularly if you have a CX.

You did not say why this was the case. You were called out on the last "particularly if you have a CX" comment - the current consumption is not an issue. Others replied with positive experiences using rechargables. You then replied several times with fairly angry replies, said you were leaving, then deleted the replies.

Again, it is hard to find evidence of your subtle insults in your old posts, because you've deleted them from the public record. I remember you often replied in an insulting tone.

Questioning people's credentials is an invitation to have yours questioned. To date no one has been impolite enough to question yours.

It's not that technical debates are unwelcome - it's that you're going about it in completely the wrong way.

You clearly have a lot to contribute. It would be great if you could do so without playing the victim and 'lashing out' at invisible enemies.

This forum is otherwise one of the most polite ones I've seen.


You have a habit of deleting your comments.

Sometimes I wish Dave would remove the capability of deleting messages. I sometimes go several days between visits to the forum, and it's really annoying trying to follow a thread with all those (deleted post)s in the middle. Fortunately, people other than Don almost never delete anything. If I ever feel the need to respond to one of Don's messages, I'll quote the entire thing to ensure the context doesn't "disappear" later.


Hi, Brian;

I have some Gama-Power AA-size batteries and I'd like to know if the N-size you mention are also made by Gama Power as well (the GP made me wonder...)

Were I am in Brazil (a small city), it is hard to find either regular, alkaline, NiCad or NiMH N-size batteries, and I had to ask for some local suppliers to try finding some for me. One of them found five packs with two (Eveready's Energizer) and I bought them all. Not cheap, somehow expensive.

That's the main reason I`d like to try some N-size MiMH. I actually built a pack of four regular D-size batteries with a home made connector so I can power any HP41 with the small, gold coatted ball+spring set (those who deal with the earlier fullnut models know what I mean). I use the D-size battery pack anytime I want to use the card reader, the wand or the 82242A (IR printer module), and the four beasts have been down yet. The last time I measured the voltage in their terminals when using the card reader (VER), I read 5,86 volts. And they are in use for about one year! I must confess that I do not use the HP41's in a daily basis, but the D-size batteries have not even signed they are about to be exhausted... Although I like very much the solution, it is not exactly cosmetic and space-saving. And the handheld use is limitted to the wiring.

I'll add some pictures as soon as I have an acceptable holder for the D-size pack (I simply clampped the plastic halves of the original package together... Shame on me!). Meanwhile I'll try to locate the N-size NiMH, now that I have an identifier.

Thanks and best regards.

Luiz (Brazil)


Hi Luiz

I am not sure of the manufacturer but here is a picture of the cell type I obtained from Strikalite here in the UK.

I hope this helps but, if not, please get back to me.



Hi, Brian;

thank you so much for adding this picture. I downloaded it will print (good image, indeed!) so it is easy to find a 'match'.

As I succeed finding (or not finding), I'm posting again.

Thanks a lot!



The manufacturer of these batteries is GP Batteries in Hong Kong. They list the GP50NH N cells and the GP23NH 1/2 N cells (for HP41 battery packs rebuilds) here:

where there are data sheets.

I have not yet found anyone who can supply the GP23NH.



Does the IR module really use so much power?


Hi, Gunnar;

I have no figures available (curent consumption), but I use a lot the IR output so I can capture program tracing with an HP48 so debugging is a lot easier. This way, as a program runs, the IR module outputs each step and each new X-register contents. I know that I had a pack of four alkaline N-cells exhausted in less than three months after debugging many programs. I generated a lot of trace output, though, and the HP48G+ was connected to a small laptop so I could trace the HP41 program and see the complete trace listing in the computer screen a few minutes later.

Maybe it is not too much of power consumption, but I use it too often, you see?

Best regards.

Luiz (Brazil)

Edited: 26 Oct 2005, 5:03 p.m.

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