Power management issues with Trisquel Mini 5.5

I use Trisquel on a low-end netbook. The Gnome edition works fine, although it is a bit slow. The Trisquel Mini edition is significantly faster, but power management is an issue : the LXDE battery indicator gives wrong numbers, and the battery discharges itself completely when suspending the netbook for a while.

I have tried to use gnome-power-manager. The package is indeed installed, but /usr/bin/gnome-power-manager, which I would have liked to launch at startup, does not exist.

I can manually launch xfce4-power-manager, and then a seemingly functioning battery indicator is added to the tray, but I am unable to launch it automatically at startup, by adding @xfce4-power-manager in /etc/xdg/lxsession/LXDE/autostart.

Any ideas? Thanks!