I've given up on making my own mod because it was getting dangerous. I will however share how easy it was to do a USB recharging circuit. First, google
MCP73855
I actually cheated and used their Evaluation Board. The guide to using it is here:
http://ww1.microchip.com/downloads/en/DeviceDoc/51522a.pdf
It's about 2 inches by 2.25 inches, and not very thick. Initially this was perfect as it was roughly the same size as the NP-60 batteries I was attempting to use. Using the guide though, it was very easy to incorporate this circuit in my design, and was only 25 bucks for the evaluation board. If you are skilled with doing your own circuits, you can get the chip itself for under two bucks, and get a sample sent to you for I assume nothing.
Eval Board:
Product Search - microchipDIRECT
Sample Chip:
Microchip - Samples Web Site
Hope This Helps
MCP73855
I actually cheated and used their Evaluation Board. The guide to using it is here:
http://ww1.microchip.com/downloads/en/DeviceDoc/51522a.pdf
It's about 2 inches by 2.25 inches, and not very thick. Initially this was perfect as it was roughly the same size as the NP-60 batteries I was attempting to use. Using the guide though, it was very easy to incorporate this circuit in my design, and was only 25 bucks for the evaluation board. If you are skilled with doing your own circuits, you can get the chip itself for under two bucks, and get a sample sent to you for I assume nothing.
Eval Board:
Product Search - microchipDIRECT
Sample Chip:
Microchip - Samples Web Site
Hope This Helps
