To securely charge a lithium ion battery, you need to adhere to the right billing procedure, which includes a constant-current phase adhered to by a constant-voltage stage. If you simply make use of a constant-voltage source, you'll wind up charging the battery faster than it's made to deal with. The second line means that under no conditions I ought to boost the input billing voltage beyond 4.2 V, else it could damage the battery. Totally draining pipes the batteries breaks down the crystals to their original state.