Androidémon Healing Center is a fun way to test the waters that is Tasker.
What this project does is when your device is plugged in your device will say "Healing started" and every 5 minutes it will read your battery level and compare it to the last. Then it will say the difference between the two levels "Health restored by X" where X is the difference. Then when the device is all charged up it stops reading the battery level and says "Your Androidémon is all healed up".
Simple but fun way to get dirty with Tasker. If you just want the application without all that Tasker stuff grab it from the release page here https://github.com/Korpip/Android-mon_Healing_Center/releases