Battery Polarity


I have a number of HP calculators without battery packs.

I know that I should be careful with battery polarity, so I'm going to ask first before I try things:-)

The first is the HP21 and HP25C (I'm assuming the battery polarity is the same.) If I look at the back of the calculator, with the top of the calculator pointing away from me, the contacts are at the bottom (toward me). From what I can dertermine, -ve is to the left -- is this right?

And then the HP34, 32, 31 type. Again looking at the back of the calculator, top away from me, the contacts are on the left top corner. If HP were consistent, I'd assume the top one is -ve and the bottom one +ve. Am I correct?

I'm planning on using rather flat 1.5v cells initially to try them out. Later I will try to fabricate somethng from nicads.


Figured it out!


If anyone else is curious, there is some information at:


And very good information it is too!

After I searched (probably badly :-) some of the archives, I had a bit of a snoop around and found the annotated images.

Just what I was after!

I have another question, but I'll snoop around some more first. Maybe I won't look so foolish :-D


I wouldn't consider somebody foolish, just because he/she didn't find something here on the website. I've seen the site growing over the years and there are lots of info stored somewhere in the pages - thanks Dave !

I also have to look around sometimes, when I remember, I've seen something, but don't know exactly where, so you even should ask, so that everybody can learn...

Though I began posting here 2 or three years ago, I watched the site much longer (I just didn't feel "qualified" for posting here in the upper league - this changed a little when I actively began collecting). I even remember the time, when I saw the page the first time - seems like I used the then new Netscape 3 - or even Ver. 2. The site didn't have this fancy URL, but I don't remember the old one.

Dave, when did you start this site ?


Hey that's answered in the FAQ you know! ;-)

OK the site went "live" in May 1995. I probably started thinking and planning around Dec 94/Jan 95. It took some start up time because before starting the web site, I only had the few HPs that I just happened to have - very small and random bunch. I wanted to have all the scientific classics and woodstocks to start the museum. After I launched it with those, I got many messages along the lines of "Great! Wonderful! Hey where are the rest of them?" The collection was completed in early 1996. Since then, it's mostly been more details, software, etc…

Friends and coworkers thought I was crazy because in 1995 they thought the whole web/net thing was a fad. (A little later my company overreacted in the opposite direction and put the word Internet into the plans of every single group.)

The site was all coded by hand (no HTML editors yet) and still mostly is today. The original pictures were scanned on a flat bed scanner at work after hours. A scanner of my own seemed much too exotic and expensive in 1995. Pictures were carried home on conventional floppies and uploaded over an analog 33K modem. The original URL was This hasn't existed for several years but there are still approximately 400 links to it.

In 1995, I had no idea how big this site would become. I sometimes think that I should analyze all the stuff that's here and reconsider how it's organized. I'm afraid doing that might just drive me crazy however. (And maybe the long time visitors too.) Hopefully the search function on the main page helps new people. Assuming they find that :-)


...and after all this work my wife thinks I am crazy because I spend time visiting your site and collect old machines.
Thanks Dave.

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