You know, it would not take much of a mechanical genius to simply install a couple of extra batteries in any vehicle. Off-hand the materials required: Battery boxes, fabric straps, extra cable couldn’t be terribly expensive.
The real question, of course, is, what the hell are you people doing living in such cold frikken’ places?
Huh? Huh? Tell me.
Ah, shaddap, melanoma-boy (though your location field says Boulder, which I thought got pretty cold at times. How ironic).
Regarding Q.E.D.'s calculation, is there anywhere in North America that charges 20¢/kW-hour? That seems preposterously high. I pay less than a nickel.
I remember a military van that had been modified so it had a big plug in the cargo area. We had two twelve-volt battiers in a big plastic tub and left them plugged in most of the time so they were fully charged. The goal, though, wasn’t cold-weather starting, but hooking up the battery tub to an inverter and running a public address system (or anything else) for hours on end.
Well, she’s getting to down to around 10 F tonight and apparently this is warm for the next week or so. Still no problems, yet. But in a few days when it hits -30 each night, my car will still start. See, block heaters are 99% standard on cars here (even used ones).
Your battery is like the reporters from Time’s Square on 12/31. Reporting on being lucky being in layered clothing because it was 42 degrees. Just weak. Go for the highest ranking cold weather cranking amps, spend the forty bucks or so on a block heater, you should be able to get one from NAPA, and any self respecting North Dakotan/ Minnesotan can set it up for free in about 8 minutes. Unless you live in the NorthEast and whine about 42 being frigid. Then you would owe us a house.
Toughen up.
BTW, Bryan Ekers, didn’t notice the kw/h. Can you beat the $.987 per unit for gas of heat? That’s USD. We now run elctric space heaters to save money. sigh Off to Nevada soon 
If you were to add and extra battery, how would this effect the alternator?
I knew I forgot something. The Block heater keeps the anti-freeze, oil, and starter from getting locked up. Yes, anti-freeze at any temp can contribute to non-starting if it doesn’t somehow keep the basics ready to go. See: thermostat. Coolant mainly helps prevent overheating and helps retain running temp heat. Ain’t gonna help if the rest of the components are frozen. That isn’t what the coolants tell you in a mild climate, but anyone in the actual -40F climate can tell you, it’s not enough.