The Museum of HP Calculators

HP Forum Archive 13

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HP21 batteries
Message #1 Posted by Bill on 6 Nov 2003, 3:48 p.m.

Hi there, new to the forum. I have an HP21 which I bought for fun at a garage sale but am currently relying upon as I lost my beloved 41CV. I don't see how to remove the rechargable AA batteries from the pack/holder. The calc. will only work now when plugged in, I would like to replace the batteries, any suggestions? thanks in advance....

      
Re: HP21 batteries
Message #2 Posted by David Ramsey on 6 Nov 2003, 4:09 p.m.,
in response to message #1 by Bill

Actually, replacing the batteries is pretty simple.

Use wire cutters or a knife to trim out the central plastic spline that runs between the two batteries.

Now you can easily remove the old batteries, clean out any corrosion, and simply insert a fresh pair of "AA" alkaline or NiCads. Make sure you get the polarity right!

            
Re: HP21 batteries - link
Message #3 Posted by jimc on 6 Nov 2003, 4:13 p.m.,
in response to message #2 by David Ramsey

http://www.hpmuseum.org/howtohp/howtohp.htm

and

http://www.hpmuseum.org/batts/battery.htm

                  
Re: HP21 batteries - link
Message #4 Posted by Bill on 6 Nov 2003, 4:43 p.m.,
in response to message #3 by jimc

I cut the back piece as shown, thanks for the help! I think the batteries I pulled out are circa 1975 like the calculator

                        
Re: HP21 batteries - link
Message #5 Posted by R on 6 Nov 2003, 4:46 p.m.,
in response to message #4 by Bill

Be sure to clean off the battery terminals of the pcb from corrosion, if applicable;-)

Raymond

                              
Re: HP21 batteries - link
Message #6 Posted by Bill Plaxton on 6 Nov 2003, 6:00 p.m.,
in response to message #5 by R

ok now here's a dumb question, can I run nickel-metal-hydride batteries in place of the NiCDs which I haven't been able to find? thanks again...

                                    
Re: HP21 batteries - link
Message #7 Posted by David Smith on 7 Nov 2003, 3:19 p.m.,
in response to message #6 by Bill Plaxton

Yes, NiMH cells work wonderfully in these machines. 1800maH cells will run it for three times as long as the originals (if you charge them for three times as long).


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