Heat kills, and on battery power efficiency is king. ENERGY STAR rates this inverter window AC at 15.0 CEER, better than the heat-pump window units we found on Amazon, and it draws about 710 W at full cooling (per the listing), less once the room is cool. It doesn't heat, and that's no loss: Midea's heat-pump version stops heating below 41°F outside, which is when cold turns dangerous.