The phone will stop charging when full and switch to a standby mode to protect your battery. This is all done in the phone rather than the charger -- the technology is pretty sophisticated. And no, I've not noticed any issues. I charge with a Tylt at home (all night, 8 hours or more) and an older Qi Infinity charger at work. Both are 3-coil. My current and previous phones were both charged wirelessly nearly 100% of their life.