HP-41C rechargeable batteries

Everything about 41C 41CV and 41CX Hardware

HP-41C rechargeable batteries

Postby makbil » Sun Apr 25, 2010 1:54 am

It took me a while to find these so I thought I'd share the information.
This site has NiCad rechargeable N size batteries available to replace those in the HP-41C battery pack.
It's next to impossible to find these so I've ordered a set. I should receive them within a few weeks, I'll post the results.
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Re: HP-41C rechargeable batteries

Postby Garth » Sun Apr 25, 2010 3:22 am

Have you tried the rechargeables? My 41 shows "low battery" at the voltage that rechargeables are when they're fully charged. Both NiCd and NiMH are 1.2V, so my low-battery indicator would be on full-time. A $5.00 set of alkalines lasted me a couple of years in the 41cx until I got the double extended memory module, and now they seem to last six months. I wouldn't want to be constantly thinking about having to recharge.
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Re: HP-41C rechargeable batteries

Postby makbil » Mon May 10, 2010 9:59 am

I have ordered 2 sets of batteries and a charger which I should get today. As soon as I try them I'll let you know.
As far as I know, the 41C was designed for NiCd batteries as NiMH was not available yet and at this time it is impossible to find any NiCd rechargeable batteries. This may make a difference as the characteristics of these two technologies are not identical.
I'm also looking at some batteries to replace those in the rechargeable battery pack, mainly the Varta 422-371 but I need to find someplace that has international shipment options.

Edit 1: Got the batteries (they are NiCd batteries after all), charged them and when I put them in my HP-41CX, I don't get any low battery indication.

For those who may be interested, these are what I got:

Batteries: (NiCd 220mAh) $1.95 each
http://www.batteriesinaflash.com/assemb ... n-top-cell

Charger: $26.95
http://www.batteriesinaflash.com/batter ... -batteries

Edit 2: Initially I had some problems with the screen going nuts when doing some operations but after thoroughly cleaning the contacts everything works perfectly now. What's left is to fix my card reader now :)
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Re: HP-41C rechargeable batteries

Postby sm5hua » Sun Jul 08, 2012 9:07 am

Hello

I am using GP 50NH NiMh 500mA batteries in my CX and they work perfect...

http://www.gpina.com/pdf/GP50NH_DS.pdf
http://www.smallbattery.company.org.uk/sbc_N_NiMH.htm

Regards: Peter
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Re: HP-41C rechargeable batteries

Postby arlenbaker02 » Wed Jan 30, 2013 6:45 am

Philips rechargeable batteries is perfect using brand today's, Now you ordered okay so keep sharing your though with us through this wonderful section.
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Re: HP-41C rechargeable batteries

Postby Garth » Wed Jan 30, 2013 7:00 am

arlenbaker02 wrote:Philips rechargeable batteries is perfect using brand today's, Now you ordered okay so keep sharing your though with us through this wonderful section.

That particular page does not have the right size.
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Re: HP-41C rechargeable batteries

Postby anetzer » Sat Jun 08, 2013 5:28 am

Just a few thoughts: There seem to be many slim and simple (micro) USB charging pcb's on the market.

http://www.hobbytronics.co.uk/usb-lipo-charger

(I know this one will not do the job, but it is the smallest and most encouraging I could find on the fast ,-)

Add an appropriate block of lipo batteries and you should be able to fit the whole thing ion an oem battery holder and if all goes very well you could even charge it, while it is connected to the calc and rund the calc of the USB...

Am I to optimistic?

Greetings,

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Re: HP-41C rechargeable batteries

Postby Garth » Sat Jun 08, 2013 7:53 am

anetzer, the voltage of a single lipo battery is not enough to run the HP-41 on, and two lipo batteries in series is too much, giving 7.4V, up to 8.5V when charging, which stands a chance of damaging your 41 if you modify the battery holder to take these. It's the same story for Li-ion. Four alkaline cells (which the 41 is made for) give 6.4 absolute max when they're new, and four NiCds give about 5V with a full charge. I would say lithium batteries are absolutely out. Don't risk damaging your valuable HP-41!
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Re: HP-41C rechargeable batteries

Postby anetzer » Mon Jun 10, 2013 8:30 am

Garth wrote: Four alkaline cells (which the 41 is made for) give 6.4 absolute max when they're new, and four NiCds give about 5V with a full charge.


Thanks for the enlightening remarks. Didn't know that lipos don't come in other voltages too. But even if it is Alkaline or NiCad: What about a USB-PCB to charge? Those should be fairly common to get hold off and one would be able to charge from the PC or with any iPad or Micro-USB charger?

I ask because I do have an HP 41 with a battery tray and am contemplating alternatives to buying a refurb battery pack and a used charger for, well,150 bucks minimum, if eBay is to be believed...
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Re: HP-41C rechargeable batteries

Postby Garth » Mon Jun 10, 2013 10:00 pm

anetzer wrote: But even if it is Alkaline or NiCad: What about a USB-PCB to charge? Those should be fairly common to get hold off and one would be able to charge from the PC or with any iPad or Micro-USB charger?

I don't know if they're available, but it sounds better than having a separate charger that requires removing the batteries from the 41 for an extended time to charge them. If you had to remove them for charging, you'd definitely want two sets, so you could swap them out so as not to leave the calc unpowered and lose memory. I wish lead-acid batteries were available in really small cells, because lead-acid has a very slow self-discharge rate (unlike NiCd) and the charger does not require any intelligence. Three in series would give 6V, like four alkaline batteries in series.

Energizer N-size alkaline cells are available at Digi-Key for $0.85/ea for 10 (I would buy 12, for three sets, which would last years), at http://www.digikey.com/product-detail/e ... -ND/704824
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Re: HP-41C rechargeable batteries

Postby scan80269 » Mon Jul 08, 2013 3:03 pm

This is my first post.

I have found a source for N-size 500mAH NiMH rechargeable batteries for the HP-41 in the U.S.:

http://ogazent.com/cscart/index.php?dis ... egory_id=5

They also have N to AA battery adapters to allow the N-cells to be recharged with a AA NiMH battery charger. I use a MAHA MH-C9000 charger which has an option to set the charging current down to the 50mA setting needed for these batteries. This charger was bought from http://www.thomasdistributing.com

These rechargeable N-size NiMH batteries are far more economical to use with HP-41 than disposable N-size alkaline cells.
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Re: HP-41C rechargeable batteries

Postby StickyFox » Sat Aug 23, 2014 11:27 pm

Thanks sm5hua for the link to the batteries ... I was having a hard time finding anything suitable! I did see rechargeables on ebay for £55 a pair ... :shock:

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Re: HP-41C rechargeable batteries

Postby Garth » Sun Aug 24, 2014 2:08 am

I'm not quick to recommend rechargeable batteries for the 41 unless you're using the card reader or the bar-code reader wand a lot. My own 41cx went two years on each set of alkalines even with everyday use, until I got a double extended memory module which seems to have more leakage current and took the battery life down to around six months on a set of alkalines, again with everyday use. If you use rechargeables, you'll have to have two sets if you have to remove one set to put it in the charger, using the second set to preserve the memory while the other set is getting charged. The price of two sets of rechargeables plus charger will buy many, many years' worth of alkalines, and the rechargeables need more-frequent attention because of their self-discharge rate. Yet another point is that if the rechargeables are 1.2V, my own 41 would show the low-battery annunciator all the time, because it comes on at 1.2V. Again, I don't recommend rechargeables unless you often use the card reader or the bar-code wand. I have the tape drive, but I have enough memory in my 41 to perpetually keep everything I need in it, so I virtually never have to access any kind of external storage.
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Re: HP-41C rechargeable batteries

Postby StickyFox » Sun Aug 24, 2014 10:23 am

Garth,
Excellent advice .. I only recently found out you could get such a thing as a N cell chassis. So I assume no-one really bothers with the original HP chargers, either then. This is all great news, looks like with an alkaline battery chassis, you can carry on for years at negligible cost. I was freaking out because I couldn't replace the native rechargeables!
What's a sensible inspection period to check for leakage? 6 months?
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Re: HP-41C rechargeable batteries

Postby Garth » Sun Aug 24, 2014 3:12 pm

StickyFox wrote:What's a sensible inspection period to check for leakage? 6 months?

Since mine turns on the low-battery indicator at 1.2V which really isn't very low (like a 9V battery being down to 7.2V), there seems to be no danger of leakage at all if I replace the batteries when it comes on. I'm sure I could continue to use them for a long time after it comes on, but then I would have to check frequently for voltage (to make sure I don't lose anything in memory) and for leakage. I have never seen any leakage. I've been using my 41cx every day for 28 years.
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Re: HP-41C rechargeable batteries

Postby StickyFox » Sun Aug 24, 2014 10:04 pm

Sorted - thanks! Every day, huh? 10 to the four days. That's a lot of RPN.
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