I bought a space heater for the car and posted a link awhile back. The thing was made in China and it is dangerous. The fan stopped, the coils started glowing red and smoke came from the plastic cover. It does not appear to have an overheat shutoff like every hair dryer.
The older heater I got from Napa years ago seems very safe but appears to be discontinued. I hear it cycling off and on as the car gets very warm, so I know the safety sensor is working. I suspect it was from ZeroStart, which is a Canadian arm of Phillips Tempro. They still offer a better model with a metal case:
Looks to be around $110 but if it does not set my car on fire, it might be worth it since keeping the batteries warm is giving me Great Range! Every one else is complaining but I am getting the best range I ever have even in this cold.
The northern Europeans seem to have more choices for car interior preheaters. They cannot afford to warm their cars up by idling since the fuel prices are higher there. But the DEFA brand of heaters does not seem to be available in the US.