Laptop does not shutdown/hibernate on critical battery
This is how I fixed a problem on my Toshiba laptop which wasn't hibernating on critical battery.
If the laptop does not shutdown or hibernate on critical battery it can be the ACPI implementation causing problems with the "time remaining" features.
I fix the problem on my Debian installation by changing the Gnome Power Manager configuration.
I opened the gconf-editor and unchecked the following keys:
/apps/gnome-power-manager/general/use_profile_time
/apps/gnome-power-manager/general/use_time_for_policy
This also fixed the gnome-power-manager tooltip which it wasn't showing up.
I suppose that this it will work also for Ubuntu.
Danilo