Hey there!
So, I might get my hands on like 2 of those Adapter PCBs for the Extensions Pins in the phone.
Once I have those I could probably experiment around a bit with using 18650 batteries (or similar) with a FP2.
The challenge I see in this is following:
- Build a circuit to safely charge and balance the batteries
- Include protection circuits for Li-Ion batteries OR use Li-Ion batteries that come with such circuit
- Adjust the Voltage to fit with the original battery of the phone
- Make it connect to the Extension Pins
- Create a suitable phone case, maybe one you can easily attach and detach from the phone when needed
- Maybe make it so that those batteries only act as a covenient way to charge the original battery instead of running the phone on them.
(No idea if the Android System would be happy about using 18650 batteries, original battery also has 4 pins, have to look up what they are used for.)