I have my cars dash to 12v socket plugged into the car and sat next to it is a powerfull power pack with a usb lead attached to it going to a female 12v adaptor
When the car is left in a car park simply pull the cameras male 12v out of the car and shove it into the power packs female (cigar lighter ) adaptor
This can run for days I imagine but have only used it for 2hrs at a time max
Otherwise
My car spends most of its life on my drive