i know what are you talknig about, and that's NORMAL: every android phone does like that, if you reboot your device while it's in charge, the calibration charge is messed up, so do NEVER reboot your device so often...if you forced to do that, so wait until it's 100%, wait something like 1/2 hour / 1 hour at least and then disconnect your phone from the charger. Then use it until it shut off for low battery (and even in this case, just ONCE you have to make it shut off or you will cause damage to battery.
That's it, i hope it helped