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How to make a laptop start on a lead-acid battery?

By wondra ·
Greetings,
I got a Dell Latitude CPi-A with a dead battery. The computer is no longer worth the cost of a new one, so I tried a trick I used on a laptop with NiMH batteries before - run it on a cheap external lead acid battery (12V 7Ah, sustains a laptop for quite a Long time).
However, with the old laptop it was sufficient to leave the thermistor in place for the computer to recognise the battery and boot, on the newer laptop with the smart battery interface, this didn't work. I connected the external source to the laptop through the charging circuit (or without it) and the best I can get is start the notebook on the original PSU, then remove it and it runs from the battery, but it won't boot with just the battery.
Any insights on how to start it? Do I have to program a microcontroller to behave like an always-full SMBUS battery or is there an easier way?
Thanks, wondra

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FIrst thought::

by 1bn0 In reply to How to make a laptop star ...

off the top of my head.

Disassemble the old battery and remove the cells.

connect the external battery to the connectin points of the old cells?

Don't know if that would work but it was the first thing that popped into my head.

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FYI, the battery is available for $64 on many websites. No text.

by CharlieSpencer In reply to How to make a laptop star ...
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Is this as simple as

by The 'G-Man.' In reply to How to make a laptop star ...

just having the end of the PSU plugged in to make the battery work. If so, get an old one and cut off the wire.

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You just need more current

by robo_dev In reply to How to make a laptop star ...

12V @ 7A is only 84 watts, but most laptops need around 130-160Watts to boot. Plus most of them run at 18V, so 12V may be on the ragged edge of what the mobo regulator can handle.

A pair of 7 Amp batteries in parallel would give you around 170W, which would probably work.

Although it's entirely possible that the little regulator chip on the laptop motherboard would fry since it may not like only 12V instead of 18V.

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