As long as it is the same size iBook, i.e. 12" to 12" or 14" to 14" the battery is the same. I use the battery from my 12 G3 500 in my 12" G4 no problem.
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PB G4 15" 1.2ghz - Pismo G3 400 mhz - iBook G3 500 "Jukebox"
"SawSmurf" G4 500 - Quicksilver G4 Dual 1ghz modding...