Windows continuously monitors the power level of your battery and warns you when the battery power reaches low and critical levels. When your battery charge gets low, the battery icon on the Windows taskbar indicates a low-battery power level. Make sure that you have sufficient time to install a fully charged battery, find an AC power outlet, or save your work and turn off the mobile PC. When your battery is almost out of power, the battery icon changes to indicate a critical-battery level.
Open Power Options by clicking the Start button , clicking Control Panel, clicking System and Maintenance, and then clicking Power Options.
On the Select a power plan page, click Change plan settings under the selected plan.
On the Change settings for the plan page, click Change advanced power settings.
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.
Click OK to save the changes, and then click the Close button on the Change settings for the plan page.