Thanks to all posters thus far.
Spanner - you are correct - but I primarily want to use it/them for illuminating LED lights whilst camping and recharging bluetooth gizmos, and if I have to have the ignition on, then I also have to have the headlights on. Not good.
I generally don't forget items that are plugged in as I am usually eagerly awaiting them to be unplugged again for use.
I like the idea of one poking out from under the seat that may be tucked away when not in use too.
Will look into USB/cig lighter combo units as well.
Cheers, Diesel