Mains adapter/charger for HP-67 and HP-65?

[Dave Britten]

Conventional wisdom is that you're better off not plugging in your HPs these days. The 65 and non-programmable Classics are allegedly fairly resilient, but with the 67 being based on Woodstock technology, I would be very nervous about killing it if it's plugged in and the battery isn't connected securely.

I just use Eneloop AAAs in my Classics, with one of Mark Hoskins' excellent AAA battery cases:

https://www.ebay.com/itm/323932408596

A modern AAA NiMH (~750 mAH) should have capacity pretty comparable to a 1970s NiCd AA (nowadays 600-1000 mAH). You can get Eneloop Pro AAAs if you want 950 mAH.

I like this setup so much that I made a similar AAA case for my TI-59, though it's not quite as pretty as Mark's.

If you still want to get some use out of the NiCd packs you already have, I'd probably try to track down one of those HP spare battery chargers (or just make one, since NiCd charging isn't terribly sophisticated).