Mileage per liter of fuel with combination engine

As far as I can tell, if you use an electric engine (large or enhanced, likely) as your actual engine, but add a small gas/diesel engine with all possible generators attached to re-charge the batteries, you can get WAAAY better mileage per liter of fuel than if you used that fuel to drive the MAIN engine itself.

To clarify how it works: you only leave the main electric engine ON when you drive, and when you park you disable the electric engine and enable the combustion one and let it run at idle while you do whatever it is you came to do. You can get 2+ full storage batteries out of 5-10 liters of fuel that way, and from my calculations two full storage batteries provide much MORE of watt-hours of engine power than 10 liters of gas if used directly in combustion engine.

Is this intended? Or are my numbers just way off and large combustion engines are nowhere near as fuel-intensive as I assume?

So I checked the numbers, and in 0.C-6513 (with vehicles pack installed) large electro engine lists 40 000 e-power consumption giving 400 normal power.
While a gas-powered engine can generate ~12 000 e-power with all generator types installed.
I’m not sure how well gas consumption is tracked, but it’s linear with engine power afaik, and theoretically you need less than 30 normal power to run those generators.
So it’s about 100-110 units of normal power via gas engine to produce e-power for 400 power electro engine.
And it’s even better for smaller electro engines.

Need to check that those numbers apply without the vehicles pack, ISTR that mod messes with efficiency to buff vehicles. Why vehicles need buffs IDK.