Square mil, and square mil-e[quivalent], for the battery-only efficiency, not miles. When you have a volume-per-distance measurement, such as liters/km, you ca

Square mil, and square mil-e[quivalent], for the battery-only efficiency, not miles. When you have a volume-per-distance measurement, such as liters/km, you can cancel units to get an area. The square mil -- a mil is 1/1000 of an inch, usually used in machining parts -- is the US customary unit which is best suited to the magnitude; 62 square mil is so much nicer than 0.04 square millimeters or 40000 square micrometers.