If you did it often enough, and for long enough, it would eventually affect your battery. I found out the hard way, when I had a flat tire and I had to fill it every day with an air pump that plugs into the car. It was about 4 years old and working perfectly, now it is very very weak. My advice to you is to get more blankets, or a very thick sleeping bag.

simple answer, it would, so start the car, let the battery charge up every 30 minutes or so, or pay the $ for a second deep-cycle battery with switch to keep the primary batt. okay. Old SUV trick.

You can get a "Battery Buddy" or "Battery saver" that you can install easily and they dont cost that much. It will shut everything off when your battery gets low enough, but still leave enough to start your car. I had one on my semi truck. they work great.

the electric blankets that i have seen are for ac electrical. the car uses dc. it may not even work.

Probably

You have about an hour.

I'm thinking about getting a electric blanket for my car (I do a lot of work out of it it's like my office when I'm not working) I don't like to let the engine run all the time if I'm parked.

So I was wondering if the blanket would draw too much from my battery so that it wouldn't start the car?

I have a standard 840CCA 12V battery the blanket would draw a constant 4 amps for 30 to 45 minutes. Would it kill my battery?