Do portable 12 volt car heaters work?

Portable 12-volt car heaters can provide some warmth, but their effectiveness is often limited. They typically draw power from the vehicle's electrical system, which can lead to a slow heating process and may not heat a car's interior sufficiently in extremely cold conditions. Additionally, they are generally less efficient than a car's built-in heating system. For short-term use or in mild conditions, they can be useful, but for optimal heating, it's best to rely on the vehicle's heater.