Once the battery reaches 100%, wired or wireless, charging stops. The only problem with a wireless charger is that current is still being drawn from the charger, so you have 2 "problems". 1. You're paying for power that's not doing anything. It's being drawn from the charge plate, going to the phone, but not being used. And 2. some (you'll have to check yours) wireless charge plates throw off quite a bit of heat. If yours does, and the phone is sitting over that heat source for hours or days, it's bad for the battery and for a few other components. That said, I've left my phone on a wireless charge plate for days (it gets about 5° F warmer than the table it sits on) and it's had no bad effect at all, except for probably a few cents of wasted electricity.