Since this old thread got revived I thought I'd pass along my cig lighter plug story from a few days ago
I wired up a harness to power a model airplane battery
charger from the the rear power outlet in my Jeep. It's fused for 20 amps. The charger, as programmed, draws 6ish amps while putting 5.5 amps into the battery
I noticed the adapter I got at Autozone felt warm after a few minutes, pulled it out and found the positive terminal on the end too hot to touch. Scary.
I cut off the cig plug and wired my charger cord to a seven pin trailer plug. No heat and the charger sees 11.9v instead of the 11.1v with the cig plug.