USB 5V 2.1A Charger Destroys Device
This could be caused by:


faulty or low quality battery
faulty external power source (5V 2.1A) which could push more than 5V and so fry circuitry inside your device
faulty or low quality charging circuit inside your device which could stress the battery (it could push more than 4.2V to li-ion battery, or could push excessive current to the battery)