The GP2X range of handhelds has been designed to work on 2 AA-sized batteries (preferrably rechargable but Alkaline type batteries are also supported) or on external power from an AC adapter. Since it's release, people on this board or elsewhere have been studying on ways to improve battery life and/or efficiency. After I studied the datasheets of the voltage converter chips used in the F100 and F200 some time ago for repair purposes, it turned out that the main voltage converter operates most efficiently at an input voltage of 3.7V. Other people have also experimentally discovered this, by modding the GP2X to run off 3 AA rechargables (the thread still can be found on this board, use "search" if you want to read it back) and getting more than the expected 50% lifetime increase. Inspired by this knowledge, I've been looking for ways to extend my F200 with a 3.7V battery. The most important conditions for me where that: The F200 should look completely normally from the oudside. No loose batteries, no cables, no bulges It should still be possible to operate the F200 from AA batteries It should be easy to recharge the battery. Preferrably in the F200 by using the AC adapter, but an external charger is good too. It should not fry my F200 After studying several possibilities and comparing several batteries, it seemed the NDS Lite battery suited my needs. I bought a 2000 mAh battery from Dealextreme.com and an external charger (USB or NDS AC adapter powered) from Psxboy.com (Psxboy didn't have powerful replacement batteries and Dealextreme didn't have the charger anymore ). However, the battery didn't exactly fit in the F200's battery space and I needed spring contacts. Because the battery had to be removable, soldering the battery was a no-go. So this is what I started with: the battery, the charger and the F200 Here's where it goes wrong, the battery is slightly too large. So I have to cut away some plastic to make the NDS battery fit. Here the F200 is still unharmed... After cutting a slot, the battery fits smoothly. The slot when looking at it from the inside and outside of the case.