1999 Apple Power Mac G4 converted into a Gaming PC - Started this project back in 2016 and now it's finally finished! Though not technically a Mac anymore, I thought the r/Mac
Battery for Apple 820-1814-A A1107 A1085 A1139 PowerBook G4 Aluminum CMOS RTC
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Power Mac G4 M5183 Internal Battery Replacement - iFixit Repair Guide