There's no reason why it shouldn't work - the G3 batteries don't have any "smart" internal management like the 5x0s. Assuming their cells and workmanship is up to scratch.

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Rechargeable lithium packs need smarts to prevent "rapid uncontrolled disassembly" . I haven't cracked open a G3's pack, but it would surprise me not to find additional smarts inside. But it is fair to say that the 5xx powerbook smart batteries were not very smart. They certainly were/are frustrating!