For some reason, Windows 7 (and Vista) does not allow setting the Critical Battery Action to “Do Nothing”. You may wish to use this if the Advanced Configuration and Power Interface (ACPI) in your laptop is reporting your battery charge level incorrectly. My poor old IBM ThinkPad T30 has this issue. Very annoying. The tool we will be using that comes with Windows 7 and Vista is powercfg.exe.
Here are the steps:
powercfg -setdcvalueindex SCHEME_CURRENT SUB_BATTERY BATACTIONCRIT 0
Now you can let your battery run dry properly!