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.
http://WilsonMinesCo.com (60 HP-41 links on the links page)
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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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Location: Ranas, Sweden

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.
http://WilsonMinesCo.com (60 HP-41 links on the links page)
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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,

a.
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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!
http://WilsonMinesCo.com (60 HP-41 links on the links page)
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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
http://WilsonMinesCo.com (60 HP-41 links on the links page)
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