"The MMRTG is not very efficient at turning heat into electricity. When first fueled, the thermocouples converted about 110 watts to electricity. The rover’s heat rejection system uses some of the remaining 1900 watts of heat to keep the warm electronics box warm (more on that in section 4.3); the rest of the heat radiates away into the Martian air. The rover requires 45 to 70 watts of that power at all times while sleeping.(4) It consumes at least 150 watts whenever it is awake, and up to 500 watts while driving. Therefore, the rover is completely dependent upon its batteries and spends most of its time asleep and recharging. It is active for about 6 hours of each Martian day, on average.(5)"
