You do not need to use batteries if it is plugged into the lighter socket. Like a lot of Sat Navs this model is VERY heavy on batteries. If you are lucky a set of ni-cads will only last about three to four hours. Changing settings will not make much difference. Switching off the sound might prolong them a bit.yoskiwoski said:cheers both of you. The batteries were new but not alkaliine or ni-cad just bog standard ones, I'll try changing the setting, I don't see why it needs batteries at all if it is plugged to the lighter thingy.