Calculator Security Base w/Lock

[BobVA]

You're fortunate there wasn't a battery pack in there! It certainly would have leaked by now, damaging the calculator.

The HP 35 is the first member of the "Classic" series. You can find more information about it here: https://www.hpmuseum.org/hp35.htm

Replacement battery packs are available on eBay and there are numerous approaches to making them yourself.

Depending on what happened to the battery door you may be able to repair it, and there are 3D printed replacements / CAD files available for both the door and the latches.

Nice find!