It's a good thing it only supports 8 digits... That's all the Pi I know!
A while back, I was browsing a goodwill and saw something in one bin of electronics that caught my eye. It was a vintage Commodore Minuteman 3 calculator. It had a great looking color scheme, a retro LED Bubble display, and, it was made by Commodore! So of course I bought it, even though it didn't turn on. (It was only about $3)
42 year old NI-CAD batteries are rarely found in working condition...
Upon bringing it home and taking it apart, I discovered what I had suspected was wrong with it. The 42 year old rechargeable NI-CAD batteries had leaked everywhere and were no good. So, I decided to restore the thing.
After determining if the calculator still functioned when given power (It did!), I did some research until I found out what kind of battery it uses. It's a weird 2/3 AA battery, but it's plenty common on eBay, so I bought four, enough to replace the battery pack in the calculator. While waiting for the batteries, I gave everything a thorough cleaning. It needed it.
My replacement battery pack doesn't look as nice, but it's the one that works!
Once the batteries arrived, I soldered them together into a replacement battery pack, put them in the freshly cleaned calculator, and put it all back together. It works now, without having to be plugged into a wall! As for charging, I just leave it plugged in for a day and then I can use it about a fortnight (two weeks) before it dies.
It's an awesome addition to my small stash of cool retro tech, and useful, too!
I've also made an instructable with more pictures and details on how I cleaned it and made the battery pack: https://www.instructables.com/id/Restoring-a-Vintage-Calculator/
