Lenovo P43s won't boot with internal battery connected – looking for help diagnosing battery issue

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Hi everyone,

I'm having an issue with my Lenovo ThinkPad P43s. The laptop does not power on when the internal battery is connected, but it works fine on AC power alone (battery disconnected). Once the battery is reconnected, the system becomes completely unresponsive — no lights, no fan spin, nothing.

Here's what I've tried so far:

• Power/EC reset (held power button for 60 seconds with battery and AC disconnected)
• Booted successfully on AC power only with the battery disconnected
• Visual inspection of the battery — no swelling, burn marks, or connector damage
• Battery model: L18M3P73, rated 11.52V, 4213mAh
• Planning to test it with a multimeter soon (waiting on one to arrive)

Symptoms suggest the battery may be deeply discharged or dead, but I want to confirm before replacing it. It doesn't have a test button or indicator LEDs. If anyone knows which pins to probe for voltage testing, or if there's a known issue with this battery model, I'd appreciate the insight.

Any help diagnosing this or confirming if the battery is truly dead would be awesome.

Thanks in advance!

[mon2]

Suggest to test with a known good battery. Perhaps source one from Amazon. Return it if it is not required. Wait on the multimeter to test the related parts onboard.

Would you have the schematics for this unit? Are there any silk screened markings on the board to identify the model #? So far, unable to locate a schematic for this unit.

Is it 'FT490'?

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Thanks for the suggestion! I was hoping for a "standard" method to check just the battery when not attached to the laptop. E.g. if I using the Multimeter can confirm its dead then I don't have to investigate further.

Regarding schematics a quick search gave this:
https://laptop-schematics.com/view/12463/

but seems I have to pay for it - besides the screenshots.

[mon2]

schematics & board view files are posted here:

https://www.badcaps.net/forum/troubl...rdview-request

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Probably a stupid question but when looking at that file I read:

T490/T590 Logic Schematics

but maybe its the same as my p43s?