It's irritating, every time I boot up an Ubuntu variant, it complains that my battery has a very low capacity (2,3%)
You need a program called gconf-editor to fix it, so let's get it:
Open a terminal window
type in sudo apt-get install gconf-editor
type in your password and press ENTER
now, type in gconf-editor in a terminal window.
Navigate to the Apps folder
then the gnome-power-manager sub folder
then the notify sub folder
find the setting called "low_capacity"
remove the tick next to it.
You should now no longer receive these error messages.