The 3 gallons of gas equivalent might be technically true in one context but is woefully misleading for general consumption.
Cars in the U.S. are more fuel-efficient than ever. Here’s how it happened. says fleet average is below 25 mpg.
So you tell Joe Average that your EV can store the same energy as 3 gallons of gas and he goes and tells everyone "Hur hur, that fool bought one of them EVs that only goes 75 miles." 3 x 25 = 75 so Joe Average can do the math and you let him walk away with a misconception.
Maybe if your goal is to heat a room or boil water or something that 100 kWh = 3 gallons of gas has some use as a conversion factor.
But if you can drive hundreds of miles on 100 kWh (I'd expect to get ~400 miles on that, more if it's spring/fall/summer, less if it is winter) then why ever bring up that stupid conversion factor?
I'd say the EPA should hide that somewhere in a whitepaper and not make as if that is a useful thing for consumers to see.
Even a crappy EV gets insanely good range in MPGe vs MPG of a gas car. A more meaningful metric I'd suggest they use is the average cost of electricity for the US as a whole vs consumption per mile to give you an "EPA cents per mile" instead of MPGe.
Give me EPA rated range and EPA cents per mile and that's all I need to know (and they put that on the
Monroney label anyway so I'm good.