Bad things!
Battery venting, thermal runaway, fire, vapeapalypse.....
But seriously, pay attention to how quickly and had it hits on a full battery. When you can noticeably detect reduction in the performance of the atomizer, recharge the battery. It would also be very helpful for you if you check the voltage of the battery with a fluke meter or similar so you can see where it's at before you recharge to help give you a good reference.
