You can calculate the run-time using the formula, t = (amp-hour × V)/P, where amp-hour is the battery's maximum capacity, V is the voltage of the power supply, and P is the appliance's wattage.
In the US, the household power supply's voltage is 120 V. Therefore, a 100 Ah battery can supply power for 12 hours in the US for a 1000W-appliance.
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