Thermal runaway is a significant risk present in batteries. It occurs due to a battery cell failure of some kind, occasionally as simple as the separator between the anode and the electrolyte breaking down. Once the separator melts, the cathode of the battery breaks down further fuelling the fire with oxygen, triggering an uncontrolled positive feedback loop, often leading to a destructive result. Visit website for more information: powercontinuity.co.uk/ups-maintenance-and-service/