Sometimes when waking from suspend, the panel plugin will display a very
low battery (consistently 9%), but nevertheless with a very long time
until discharged (4 hours 7 minutes, 4 hours 15 minutes, 85 hours 1
minute, etc.).

It does not match the output of commands like

$ acpitool --battery

or other battery notification widgets, so I know it isn't a hardware
problem.

Then, about 2 minutes later, the panel plugin display updates and shows
the correct capacity and discharge time.

Unfortunately, I have not found a way to reproduce it consistently, but
I did manage to take a logfile while it happened, the relevant section
of which is attached. (I can attach the entire thing if necessary.)