This 4000 watt inverter charger produces a pure sine wave, which some appliances require for use. So it can run laser jet printers, computers, televisions, CPAP machines and other medical equipment. During a big storm that knocks out electricity, a battery-bank and power inverter running a sump pump could be the difference that saves a home from flooding. The power to run a heater could save someone thousands of dollars by keeping plumbing pipes from freezing. Also great for emergency backup power applications is the automatic transfer switch on this unit, which keeps the power supply uninterrupted in the event of an outage. With the inverter hooked up to shore power, it will detect the loss of electricity and start pulling energy from a connected battery bank instead to keep the power supply constant.