The coolest RetroPie builds take a vintage console ... For this one, though, he’s using Sega’s oft-maligned Game Gear. He might actually get more than a few hours out of the battery ...
A full parts list is provided here, and thorough documentation of the power circuit is on GitHub. For a classic handheld take on the same concept, we featured two RetroPie Game Gear mods last year.
RetroPie is suited for dedicated emulation setups on devices like Raspberry Pi, offering extensive features beyond RetroArch.