A high voltage step-up ratio inverter for applications using batteries as the input power source is proposed to supply the emergency power requirement from the battery pack when the grid is down. The proposed inverter is composed of an interleaved coupled-inductor boost converter and a three-leg full-bridge inverter. Four series-connected lead acid batteries are used as the input power source. When 110 and 220 V AC outputs are required by the load sides at the same time, the 48 V DC input from the batteries would be boosted up to 350 V DC for the three-leg inverter to provide AC output power. However, if only 110 V AC is required, the proposed control strategy would reduce the step-up ratio for a lower DC link voltage of 175 V DC to enhance the conversion efficiency. Moreover, to minimize damage to the batteries, the interleaved circuit topology is adopted to reduce the input current ripple. A prototype with 400 W rated output power is finally constructed. The controller is implemented with a low-cost microcontroller, HT66F50. From the experimental results, it is seen that even under unbalance load conditions, the output AC voltage is well controlled. The total efficiency of the proposed inverter with 110/220 V AC output is 89.8%. the efficiency of inverter with only 110 V AC output is 91.1%.