I have a Tom Tom and if you connect straight to the battery the terminals will be live all the time in the base unit. As I have currently connected it all together, when I switch the ignition on the GPS will start up by itself and similarly switch off when the ignition is switched off. Live terminals tend to corrode between themselves and the pins on the Tom Tom are very close together and I would not want them live all the time. I will rewire before I go to Peterborough on Wednedsday, but the system currently works, shame though I don't want to fry the system!