Windows continuously monitors the power level of your battery and warns you when the battery power reaches low and critical levels.   If you’re like me, there is never enough time to find an outlet before it is too late and the battery dies. Did you know that you can adjust when your low-battery light comes on, giving you more (or less) time to find a power outlet?

The quickest way to adjust the low-battery warning in Windows XP:

1. press the Windows key (the key that is typically in between your Ctrl key and Alt key) and the r key at the same time.
2. From there, type cmd and hit enter. Then type powercfg.cpl,1 and hit enter.
3. Level meters will pop up and you can adjust the settings from there.

In Vista, it's a little different: 

1. Click Start, Settings, then select Power Options.
2. On the Select a power plan page, click Change plan settings under the selected plan. 
3. On the Change settings for the plan page, click Change advanced power settings.
4. On the Advanced settings tab, expand Battery, expand Low battery level and Critical battery level, and then choose the percentage that you want for each level. 
5. Click OK, and then click Save changes.