The MES 4000  is a true 12 volt marine air conditioner that DOES NOT USE A POWER INVERTER OR A GENERATOR TO RUN. It runs directly off a Marine Battery. It consumes only 18 amps on low, perfect for an overnight stay at the Lake or Ocean. As demand increases, the unit increases or decreases compressor flow to cool your cabin in the Auto mode and draws up to  35 amps on high. The unit will then cycle to low (18 amps) then blower only (3 amps) when it reaches your desired Temperature on the included thermostat. You may lock out the high setting and run the unit only on low (18 amps), and the unit  will still turn the compressors off and run the blower  if the desired temperature is reached. This unit is a great companion for larger boats if you do not want to run your generator at night and only want to cool a small state room on larger vessels or your your entire cabin on small cigarette style go fast boats or smaller Cuddy cabins. The MES 4000 cools about 300-400 square feet (depending on environmental conditions), but use the BTU calculator to be sure on your application. This unit is designed with the Off Shore enthusiast in mind, so it can handle high speed, large waves, salt water and all the seas have to offer. * when you limit the unit to the low setting.