How do I stop the battery from charging?

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http://askubuntu.com – I have a Dell Inspiron 1545 and I have Ubuntu 11.10, and in my dell laptop it allow me to discharge the battery when I am using the power cable and that helps in the life of the battery, and I used to do that in Windows. The shortcut to activate it is (FN) + (F3) but when I use it in Ubuntu it shows: AC adapter laptop battery processor and nothing helps in what I am looking for. What can I do ? (HowTos)