A cold battery has less cranking power than does a warm battery as Jack says. A cold engine, especially a V-8, has more mass to move to start and with 30 weight oil thickened by the extreme cold, will require more of that cranking power to start up. Cold batteries will go dead quicker in the extreme cold especially with a big engine. That's why a block heater is a good thing when it is extremely cold. It keeps the 30 weight thin enough to allow the engine to turn over.

Multi grade oil is a big help. 5w-30w remains fairly thin at -10F and the engine can crank.

I had a block heater in a 63 Ford Galaxy I drove in the late 60's. It was electric and it pumped hot water through the block and it did a great job. It also cost about a buck a night which in 1968 was pretty pricey. I expect they have gotten more efficient over the years. Now if it really cold I throw a tarp over the minivan and put a 100 watt light bulb in the engine compartment. The van always starts. I may be deluding myself that I am doing any good and the van would always start anyway.

If you live in a very cold winter climate, a good battry can't be beat and it is worth the extra money for the insurance.

Don