Recently, my laptop battery started getting weak (defective battery), I could no longer charge to 100%. And every time I restart ubuntu I got an annoying broken battery sign. This can become very annoying if you can not buy a new battery or fix the problem quickly. I found a way to disable this.
To do so
1. Press Alt + F2, to open run apllication
2. Type gconf-editor and uncheck / apps / gnome-power-manager / notify / low_capacity
Although this dosent solve the battery problem, it avoids the annoying little sign.