Yes, when using for 300 watts load, the general car battery can provide power approximately 25-55 minutes in the case of the engine is turned off. If the load is a laptop with 40 watts, the power time will be longer. The power inverter has an under-voltage warning and under-voltage protection circuit. If the battery voltage drops to 10 volts, the under-voltage protection circuit is activated, and the output voltage is cut off. It will prevent the battery voltage is too low and had a start accident of the car engine. If we prepare another battery and connected to the car battery, then the working time of the power inverter can be doubled.