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Disable clock battery charging

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First post, by andrea

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Hello,
I want to disable the charge circuit on a laptop that uses a rechargeable lithium clock battery (ML1220) so that I can use a regular CR1220 in its place.

The attachment Screenshot 2025-06-09 153117.png is no longer available

From the schematic I'd say all I need to do is remove R204, but before doing anything I'm asking for a confirmation from someone with a better grasp of electronics.

Or would it be better leave R204 where it is and just pull Q12?

Thank you
Andrea

Reply 1 of 2, by mkarcher

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Removing R204 wouldn't prevent current through R203 and the base/emitter junction of the transistor, so you would need to remove R203 as well. Actually, just removing R203 would prevent the transistor from opening, so if you remove R203, R204 might be kept in place. Nevertheless, you might get some leakage current through Q12, and it definitely no longer needed if you want to not charge the battey, so removing Q12 seems like the best option.

Reply 2 of 2, by andrea

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Thank you, i just pulled Q12 and it works.

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