A battery safety device and circuit which prevents detrimental effect from the three most common battery faults generally encountered, excessive heat generation, voltage reversal and short circuit problems. The device includes fast acting circuits which latch the battery in the off state until reset by removal of the load, thereby preventing continued cycling of the battery between on and off states. The safety device includes a gating transistor such as a MOSFET (metal-oxide semiconductor field-effect transistor) switch, a latching timer (RC circuit) and a latching circuit having a transistor which turns on when a charge is 0.5 volts or greater. The safety device further comprises one or more sensor switches triggered by predetermined thermal, pressure, etc., conditions, with the switches being outside the circuit (and not affected by circuit conditions) and adapted to provide a latching voltage to the gating transistor under a detected untoward condition.