Insufficiencies in Karmic's battery behavior

Caleb Marcus caleb.marcus+u-d-d at
Thu Nov 19 00:24:49 UTC 2009

Karmic's adoption of DeviceKit-Power and the latest Gnome-Power-Manager has
changed the way the GUI reports remaining battery time. The old method built
a profile of how long, on average, it took for each percentage point of the
battery to be depleted. From that, it could estimate fairly accurately,
given the user's average use pattern, how long the battery would last. This
was a huge step up from the old way of reporting the battery remaining time
reported by the BIOS, which didn't take battery charge/discharge profiles
into account and relied on current power draw measurements, leading to
unstable results. Now, we've gone back. We do profile the battery in terms
of how far off it is from the BIOS-reported remaining time, but this brings
us back to the problem with traditional BIOS-reported remaining times: the
reported time remaining can change drastically based on current usage. While
adapting to what the user seems to be doing can be a good thing, this method
leads to things like 3-minute YouTube videos or slightly long compression
operations causing a large drop in estimated battery time when in fact it
really won't have much of an impact in the long run, and the estimated time
goes back up immediately after the operation is over.

In my experience, the Jaunty behavior of profiling the battery and ignoring
brief spikes in power usage produced a much more useful, accurate estimation
of the remaining battery life. The current behavior leads to an almost
completely useless metric -- I've attached two screenshots taken during
normal usage that illustrate fairly vividly the problem with Karmic's
behavior: a) the estimated time should always go down, never go up, and b)
it should be a smooth line. Note that in the screenshots, the line goes up
and down, in one case dropping down by an entire hour and then going back
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