What will Happen if a Mobile Phone Battery THROWN INTO FIRE.. If a mobile phone battery is thrown into fire, several dangerous things can happen because most phones use lithium-ion batteries: 1. Battery Swells and Explodes The extreme heat causes the chemicals inside the battery to break down and create gas. Pressure builds up quickly and the battery can burst or explode. 2. Thermal Runaway Heat triggers a chain reaction called thermal runaway. The battery keeps heating itself internally, even i