In case you are using windows 7 on your laptop, the default reserve battery level at which you should save all the work across all the programs you are using currently, and should search for alternative power sources to plug your laptop to power to continue working on it without losing your work.
Windows warns you when your battery charge reaches low, reserve, and critical levels. When the charge gets low, the battery icon in the notification area indicates a low-battery level. When your battery charge reaches the reserve level, Windows notifies you that you’re running on reserve power.
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.
Follow the procedure to change the level of the battery it should alert you.
1. Open Start menu, type power options and select power options as shown in the image below.
2. Under Power options for the type of power plan already selected, click Change Plan Settings as shown in the image below.
3. Now click Advanced power settings as shown in the image below.
4. Under advanced power settings scroll down, open the submenu under Battery on the bottom of all the power options.
As shown in the screenshot above you can change the reserve battery level, low battery level and you can also configure low battery notification and action it should take like whether windows should hibernate, sleep or shutdown so that you can avoid losing your work.