They really should give it in miles-per-megajoule or something, though, rather than "mpg equivalent", which only serves to confuse people. What is a "gallon eq

They really should give it in miles-per-megajoule or something, though, rather than "mpg equivalent", which only serves to confuse people. What is a "gallon equivalent" of electricity anyway? Is it the amount of electricity you'd get if you burned the gallon and generated electricity at 100% efficiency? Or the amount that you'd get if you used it to generate electricity with power-plant efficiency (which incidentally is pretty high)? Or perhaps it's the amount of electricity you get if you burn the CO2-emissions equivalent amount of coal? Or the dollar equivalent amount of coal? Or... well, there's a bunch of other possible definitions.