Windows 7 low and critical battery levels cannot be set lower than 10%
Solution 1:
Search Power Options in your Start Menu and choose the first Control Panel option.
Choose Change Plan Settings on the power scheme of your choice.
Choose Change Advanced Power Settings.
Scroll to the bottom of the config box that pops up. Open up the battery section. Your options are there.
Keep in mind that some batteries have firmware that kills the battery below 5% to keep the battery from being forever destroyed or destroying the system it's being used in.