We often leave the charger on and forget in our day to day lives. It's known that the Li-ion battery will stop charging when full capacity is reached but still having at full charge for long duration at high temperatures may cause some degradation and some accidents too. Stopping between 85 and 95 may also give us extra battery discharge cycles.
So, Safe charger is an utility application which alerts you when the battery level reaches a particular range. (85 % - 95%). This application does nothing more than that :D.
How to use ?
0) Enable the alert switch from the Navigation Drawer
1) Connect to the charger
2) Continue with your day to day activities.
3) Safe Charger application will alert you when the battery level reaches the safe point.
4) Disconnect your phone from the charger :)

Note : It will not alert you exactly at 85%. (85 to 95)

For some devices,the alert may not occur when the application is not in the background, for those applications, it is required that the background activity setting should be enabled for the application in the Settings.
The settings for various devices are :
1) Samsung : Settings-> App. Settings -> Safe Charger -> Allow background activity (enabled)
2) Oneplus : Settings-> App. Settings -> Safe Charger -> Battery optimization -> Don't optimize
3) Vivo :
Step 1 => Settings -> Battery -> High background power consumption -> Choose Safe charger -> Enable
Step 2 => Open iManager -> Select App. Manager -> Permission Management -> AutoStart -> Enable Safe Charger from the list
4) Realme :
Step 1 => [Settings] > [Battery] > [Energy Saver] > Custom power consumption > Safe charger > Allow running in the background
Step 2 => [Security] > [Privacy Permissions] > [Startup Manager] > Safe Charger > Turn on

The setting will be similar for other manufacturers I believe :)

If the application still does not alert, I am really sorry for that :(
But the application will surely alert when the application is in the recent list.
Please do leave a comment in this case and I will check on it and try to fix this case in the future update.

UI credits : Incorporated the Liquid Swipe Library by Chrisvin Jem
Link : https://github.com/Chrisvin/LiquidSwipe

Source code for this application : https://github.com/AswinChand97/SafeCharger