I've already added a frontlight from a GBA SP AGS-001 and a pot for controlling brightness so I have the basics of modification down. However, I want to replace the AA compartment with a 3.7V Li-Ion battery from a GBA SP. I understand you need a protection circuit such as http://www.batteryspace.com/protectionc ... limit.aspx .
Where I get lost is how to wire the protection circuit to the NGPC PCB in combination with the battery and how to add a charging port. This shouldn't be much different from doing the same mod with an original Gameboy, Gameboy Pocket, or Gameboy Color. I also don't have an extra GBA SP to pull parts from. I just have the Li-Ion battery and a GBA SP charger. (I could really use an extra SP if someone has one they want to get rid of.)
Thanks for the help!
EDIT: This unit is for sale at the Trading Post! http://forums.benheck.com/viewtopic.php?f=11&t=41841