I think the battery in mine is kaput, if left unplugged for any length of time it would then take a very long time to recover and switch back on. I brought it in and left it plugged in to a USB port on my computer. It recognises that this is not the car as it has data lines (they are connected with resistors in the car charger). Whilst plugged into the computer USB it displays a message to say so. Now even if I unplug it that message stays on, even plugged into the car, and even more strangely the on/off button doesn't have any effect.