update on my behalf.

On paper I think my idea works.

Getting it to work is the next issue. There is very very little room to route the cables from the battery connectors to where the microusb was. I was using cables from a molex connector from a computer... which I chose as it would be best for the current. But its perhaps too thick. At one stage, if I pressed the battery into the phone hard, it would charge as I think it should (which indicates that the parts werent sitting flush with each other). But I think I need to use smaller wires.

Another challenge is the actual soldering. The alligator clips, smallest size I could find at a local electronics shop (Jaycar in Australia), were way too big. So I did some soldering attempts. The positive connection was easy to solder at the bottom. The negative connection on the other hand was a huge hassle to solder at the very bottom, as the head of the solder stick was just too wide. Can;t solder too high otherwise the battery won't fit in.

Also need to try and find a 2mm plug or something similar, both a male and female connection.