http://www.electrowarmth.com. I'll take mine over a blanket anytime. It warms the mattress not the air above where you laying. I have two and my wife and I can use them at the same time and in the morning still have plenty of amps in the battery's. I've used mine for four nights in 20 degree weather before having to recharge. That's in conjunction with everything else. Two 110 amphr battery's.
I really can't see the advantage of one a blanket. Two having to buy an inverter. Or using 110 system.