Either use gconf-editor (the nice GUI one) and navigate to /apps/gnome-power-manager/notify/perhaps_recall and set to false or use gconf2...
gconftool-2 --set --type bool /apps/gnome-power-manager/notify/perhaps_recall false
Long description of this key is:-
If we should show the recalled battery warning for a broken battery. Set this to false only if you know your battery is okay.
Which sounds like what you are asking for...