I had a Lada Niva 4WD back in the day; part of the winterization package was an extremely heavy sump.

If you perused the manual, you found out why - it suggested you light a small fire under it to serve as an outback engine heater.

The Niva was, uh, an interesting car to own, but was amazing whenever conditions turned to shite. Nothing short of an anti tank mine would stop it.

Crews did that while building the Alaska Canada highway too

IIRC, that was about heating the oil.

A long time ago, in a land far far away, I drop a fire engine. Big monster, 37 tons, with a giant v16 Rolls Royce diesel moter.

It didn't like starting in the cold, and it didn't have battery enough to crank it for long. And failure-to-start was, um, not good.

The solution was a built-in electric heater and charger. Basically it was permanently plugged in so the battery was 100%,and the engine block was "not freezing cold" (I wouldn't go as far as "warm").

Had a push button start that fired up instantly, at the cost of an extra 3 seconds unplugging it it an emergency.

My point I guess is that you don't really have to heat the garage, you just need to warm the battery up a little.

you can buy heaters that you stick into your engine where the dipstick goes for checking the oil. plug em in overnight. I'm not sure at what temperature you would also need to heat the battery; maybe the residual heat is generally enough, but the warmed engine will crank a lot easier so less strain on the battery that way.