I am still in the process of setting up the emulators and games on RetroPie so have not really done any battery life tests. However, I am using a 2000mAh Li-ion battery removed from a faulty DS-Lite console and as the whole system draws about 500mA I would expect to get 3-4 hours of gameplay IF the battery is still good.
During the setup I have found the following;
1. The GameBoy, GameBoy Color, Sega Master System, Atari Lynx and PC Engine emulators run perfectly.
2. The GBA and NES emulators work OK but have slight sound issues. This is probably due to way I have extracted audio from the Pi Zero and the known bugs in the Alsa driver.
3. The default Sega Game Gear emulator runs slightly slow, but the alternative one runs OK. However, I cannot get the alternative gg emulator to run full-screen.
4. The SNES, Genesis, WonderSwan and NeoGeo Pocket emulators run too slowly to play.
5. When using a Pi Zero through the HDMI only then all the above emulators, except Genesis, run OK. I can only put this down to the extra CPU load of the “fbcp” program driving the SPI display.
As my original intention for the Pi powered Gameboy was to only run the GameBoy, GameBoy Color and GBA emulators I consider my project to be successful. I was also surprised how well the PC Engine emulator runs which is a bonus as it has some of my favourite games. However, I might try a second one using a Pi 2 despite the potential poor battery life.
I am currently searching Ebay for another faulty GameBoy!