[ltp] Almost dead battery

[Henrique de Moraes Holschuh]

On Tue, 19 Apr 2022, Stefan Monnier wrote:
> Hmm... the Thinkpad's firmware (i.e. software rather than HW) seems to
> know about the problem (otherwise it wouldn't know to make the led blink
> orange).  So you're saying that it just doesn't bother to reflect the
> problem in the /sys data?

Depending on thinkpad version, it knows the voltage of every cell in the
battery pack *and* it has an active (command-response) i2c channel to
the battery pack controller.

If either the active i2c channel goes silent, or battery cell telemetry
received is shows a cell is bad, it will blink red.  It also does
temperature and charge telemetry, and has alarms tied to it.

If one of the cells really went bad, chances are the battery pack
controller will have bricked the battery pack (opened some protection
gates that will remain open, isulating the cells and permanently
powering off the battery pack).

This "bricking" is a safety against over-discharge and possible cell
polarity inversion (at least on Li-ION), which is extremely dangerous.
And it doesn't happen due to age: I have IBM T4x battery packs that are
nearly 20-years old and still working although at something like 20%
original capacity :-)   But it *will* happen after the cells are
degraded beyond some point for whatever reason (use, manufacture, bad
luck...), or if any of them malfunction badly.

Just replace that battery pack, really.  Or get a beefy enough power
supply that you can go without one, if that's an option.

-- 
  Henrique Holschuh