I used to root my android phone to limit battery charge + adaway. But recently I finally gave up with rooting due to all the restrictions that comes along with it.
I thought it wasn't possible except by rooting or external control. I've just been doing it manually but figure on adding an automatic controller sometime.
If you have to manually unplug that defeats the purpose. Right now I just estimate the charging time to reach 80% and set a timer to beep after that long. It works ok