Only used twice so far, both times power cuts for a day with a 200Ah 12V battery Based on the power consumption of the batteries and the output power of the inverter, it is in the efficiency range of over 90% . The sine wave looks pretty clean on the oscilloscope. I really like the built-in counter. The only concern is at the top of the title block, it says "Pire Sign Wave" in big letters. If you can't check the spelling, check the design of the device.