Whatever fits inside the current the socket, its wiring and its fuse allow — commonly modest, and published per vehicle rather than per socket shape. Heating appliances exceed it immediately; a cool box or a laptop supply generally does not.
The 12 V socket is the most convenient connection in a vehicle and one of the most limited.
What sets the limit
Not the shape of the socket, but the wire behind it and the fuse protecting that wire. The vehicle manufacturer publishes the rating, and it is commonly enough for accessories and nothing like enough for anything that makes heat.
What that rules out
Kettles, heaters, hair appliances and travel ovens, all of which are sold with 12 V plugs and all of which exceed what most sockets supply. The plug fitting is not evidence that the circuit will carry it.
What runs comfortably
A compressor cool box, a laptop supply, a phone charger, a tyre inflator within its rating. These are the loads the circuit was designed around.
When to bypass it
Anything larger goes to the battery on its own cable, fused at the battery, sized for the current and the run. That is the point at which the socket stops being a convenience and starts being a constraint — and it arrives sooner than most people expect.
What people ask before they order
Does the socket stay live with the engine off?
It depends on the vehicle, and it decides whether a solar trickle charger plugged into it does anything. The handbook says, and measuring settles it in a second.
Can an inverter be run from one?
Only a small one. Anything substantial is wired directly to the battery with its own fuse, because the socket circuit was never designed to carry that current.
Last reviewed 16 September 2026