How about a simple solution like a 2-pin CR2032 holder with a LIR2032 3,6V rechargeable battery? Would this work?

I don't think you want to charge a Lithium-Ion using the crude, constant current NiCd charging circuit on a motherboard.

There are a few hobbyist solutions to this, like "Varta Blaster" that you can search for. They are a drop-in replacement module to be soldered on to the NiCd connectors, but that have a primary battery and a diode to block charging.

Another solution is an external 3xAA battery pack soldered directly to the contacts, but with NiMH batteries in it so that they can be charged.

Be aware that with too low voltage across those contacts, the CMOS settings will stay in place when the system is powered off, but the clock will freeze in place. So you want to know if you will run into that before you go to a lot of trouble.

I found these on ebay and ordered a few to test. It's a preassembled 2-pin CR2032 holder with a diode to prevent charging the battery.

uniQ wrote on 2025-08-11, 07:15:

I found these on ebay and ordered a few to test. It's a preassembled 2-pin CR2032 holder with a diode to prevent charging the battery.

Woops, I didn't attach the image. 😁