Comment # 9 on bug 932714 from Guido Berhoerster

(In reply to David Hodgson from comment #8)
> Yes, 100% certain it was plugged into the mains for the duration.  AFAIK
> there's not a loose connection - apart from the unexpected hibernates it
> behaves as expected.  If I leave it plugged into the mains the battery never
> runs down.
> 
> There's a BIOS option to preserve battery life which is set. It may have
> something to do with it as the battery charges up to 80% and never further.
> 
> I'll leave it plugged in overnight and see when it sleeps - after 4 hours or
> 30 mins.

You can run upower --monitor-detail to observe any changes in power source and
quickly check with cat /sys/class/power_supply/AC/online whether the kernel
thinks the system plugged in or not.