dbus_battery.py

#!/usr/bin/python
import dbus

bat_bus = dbus.SystemBus()
bat_object = bat_bus.get_object('org.freedesktop.UPower',
                                '/org/freedesktop/UPower/devices/battery_BAT0')
bat_interface = dbus.Interface(bat_object,
                               'org.freedesktop.DBus.Properties')
percentage = bat_interface.Get("org.freedesktop.UPower.Device",
                               "Percentage"
                               ).real

print percentage