Whenever your laptop battery reaches to low, reserve and critical level status, the battery icon in notification area notifies you about it.

Windows 7 first indicates about low-battery level and when your battery charge reaches the reserve level, it notifies you that you’re running on reserve power. At that point, you need to save your work, and then find an alternate power source or stop using the computer.

When your battery is almost out of power, the battery icon indicates a critical-battery level, and then your laptop goes into hibernation(if activated) or Shuts down.

If you don’t have enough time to act after seeing the low and reserve battery notifications, you can increase the percentage of battery remaining for these settings. This can be especially useful for older batteries, which might not have as much storage capacity.

To change low, reserve, and critical power levels

1. Click on battery icon and open More Power Options.

2. On the Select a power plan page, next to the plan you want to change, click Change plan settings.

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, Reserve battery level, and Critical battery level. Change the percentage of battery remaining that you want for each level, and then click OK.

You can’t set the critical battery level below the minimum level set by your computer manufacturer.