...with the computers own PSU: tap some Volts through the voltage regulator to power the clock chip and add a delay circuit to power up the mainboard only a second later.

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I know I wasn't asking for help but thanks for it anyway . I had thought of hacking the computer's PSU, but I knew that the battery voltage had to be present before the main power could be applied. I didn't think of adding a delay to the main supply. You were thinking of a relay?

Having said that, however, I am now thinking of getting a proper PRAM battery :-/ , but good luck with your mac anyway.