Diamond key battery repair, other options

[oldskewel]

I have a 2001 E53 with 4 keys:
- 1 regular diamond key
- 3x key fobs made from diamond keys bought off eBay, keyless entry reprogrammed by me (not EWS), with valet keys bought from online BMW dealer (with EWS chips as provided by BMW). As shown in this photo.



Things worked great for about 5.5 years like this, but now two of the 3x key fobs have been appearing to not charge / hold a charge. I understand how they are supposed to recharge, and they worked for a while, but are now failing to work. I think the rechargeable batteries are done.

I want to replace the rechargeable batteries in those fobs. With this setup, the EWS chips in those fobs are not used; the ones in the respective valet keys are the ones the car uses. I have read online here that the tough part of diamond key surgery is to avoid destroying the EWS chip, so in my case that is not a concern.

Any detailed instructions on sourcing that battery and doing the surgery?

Alternatively, maybe easier and better, maybe I could transplant the remote/fob circuit board into a new eBay housing, maybe even with a replaceable battery vs. rechargeable. Has anyone done that?

Not looking for a repair service or programming instructions.