Powering the HP41 externally


I was contemplating fashioning a 4.8V external source for my 41's (basically 4 NiMH batteries in an external holder), and I am wondering how to hook it up.

With the battery holder out, I know that the leftmost contact is positive and the rightmost is negative, but I am wondering about the status of the middle two (negative and positive respectively) which bridge the middle two cells.

Are these two middle contacts merely a jumper to complete the circuit of all four cells? Or do they belong each to their own circuit?

In other words, when powering the 41 externally, can one use a single 4.8V source with a jumper across the middle two contacts, or does one need two separate 2.4V sources, one for the two left contacts and the other for the right two?

Forgive an ostensibly simple question. I just don't want to fry anything.



Are these two middle contacts merely a jumper to complete the circuit of all four cells?


I can confirm they are just a jumper (the central cells in my 82120A battery pack don't touch the contacts inside the calculator).

You might want to take a look at
this link.



Hi Les,

The two central contacts in the battery compartment are only used to provide continuity to the alkaline cells pack.

They have no other use nor are they connected internally. In fact, the 82120A NiCd battery pac does not have any contacts in these positions.

You can safely power your HP-41 by applying GND to the leftmost terminal and +Ve (anything between 4.8v to 6.0v will work) to the rightmost.

Hope this helps.


Edited: Oops, again late... sorry... ;-)

Edited: 17 June 2012, 11:50 p.m.

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