Who I have the same questioned this topic

Over the last couple of months, my (out-of-warranty) Droid MAXX 2 has been randomly powering down without warning. I'll be anywhere from 20% - 30% battery and a message will suddenly pop up saying my battery is at 0% and the phone will power off. Sometimes when I turn it back on it will show the real battery level and stay on, other times it'll power up showing a partial charge but then instantly drop to 0% and power off again. At that point I have to plug it in to get to to work. (When I plug it in, it always shows that it's partially charged.)

This never happens if the phone has at least a 40% charge.

Any ideas as to what is going on?