This issue started happening not so long ago. It takes too long to charge my T420 battery now. ACPI even says 90 hours, or 50 hours remaining to fully charge etc, then the AC disconnects and reconnects.

$ acpi
Battery 0: Charging, 70%, 44:24:49 until charged

Battery's lifetime is still pretty good, however. When I do some heavy tasks, the AC power dumps down to zero.

$ cat /sys/devices/platform/smapi/BAT0/power_now # idle
$ cat /sys/devices/platform/smapi/BAT0/power_now # heavy tasks

Here's TLP's output. I'm using Arch Linux.

edit: I have tested the Thinkpad with battery removed. It doesn't seem to respond bad at all, it doesn't suddenly shut down or anything like that.


Replace the power supply OR just AC cord.

That's a bad power supply, or possibly but not as likely a bad AC cord.

Good news is Lenovo uses standardized power supplies and your power supply has been around for ~15 years ! Widely available and inexpensive as an OEM replacement and aftermarket Lenovo power supplies aren't risky either.

If you have a second brick that seems to have a similar plug or friends with a similar plug, it's safe to use because they're identical. IBM/Lenovo is legendary for interchangeable components:

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Amazon sells them often for less or the same price as Lenovo.com (~$25 as of today)


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  • See my edit. Does that mean the issue lies elsewhere? – Mário Feroldi Dec 21 '17 at 1:07

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