Dash cams aren't really designed to run off battery power and those that say they do don't really have big enough batteries to be much use. Imagine recording a video on your phone for an entire commute, it would be completely dead by the end of your drive. We'd suggest getting the dash cam hard-wired in your car, it's pretty inexpensive if you go somewhere like Halfords.

Alternatively, you could power it with an external battery bank. This isn't very feasible because it would constantly need charging, but if you do go for this option - make sure you get a power bank which will support your dash cams charging capacity. As for the dash cam, I would get one that offers parking mode — which means it will turn on if it detects movement, like your vehicle being bumped. If the issue is having a 12v that's already occupied (say, by a sat nav), you could try getting a dual port 12v charger like this one we've reviewed (this will free up the 12v to let you connect two devices at once): kit.honestjohn.co.uk/reviews/review-anker-24w-powe.../