......but are there any possible problems of leaving a usb charger plugged in permanently? I have just bought a 'stubby' dual usb charger and it is small enough that I can keep it plugged in and still close the lid on it. It appears that the 12v outlet is live even without ignition on. Basically will this somehow cause battery problems (i can't see how if not connected to a device) or might I come back one day to see the car burnt down - also guess this is highly unlikely! I do kinda feel daft asking this......