Created attachment 102528 [details]
strace & sysprof logs (*.ok.* files added for reference when there's no problem)

Platform description:
This is observed on my Toshiba Portege Z30-A-12N running Debian Jessie.
Jessie comes with upower v0.9.23, however, I'm experiencing the same behaviour
after upgrading to v0.99.0 from Sid.

Problem description:
When the laptop battery approaches emptiness (capacity goes below 10% or so),
upowerd starts to consume very high CPU time --- almost one whole core.
As soon as the AC adapter is connected, the problem disappears.
Consult with Bastien Nocera at the devkit-devel ML lead to hypothesis that
excessive writing of the battery history might be the problem cause.
See strace & sysprof logs attached (these are from v0.99.0).

Note that upower --monitor[-detail] doesn't show any notable difference in
the amount of events generated (when the problem emerges).
That means 12 per 2 seconds, all 12 in one batch.