So you want to set up a dash cam, but like me, you definitely don't want to use the car's battery to power it. Most dash cams use the cigarette lighter socket, but if you do that, the drain on the battery registers on the range-o-meter as 1 mile less every 5 miles driven. Ouch.
So here's what you need...
I'm going to assume you are using a Blackvue dash cam for this purpose. So you'll need the camera stuck on to your windscreen and probably the best place for that is up at the top, next to the rear view mirror on the opposite side to you (out of your way and hidden). Keep in mind where the windscreen wipers wipe. You want the camera to be able to see out when it's raining. Next you will need a UPS (an uninterrupted power supply). I would recommend the Lukas lk-530-12v battery. Finally, roll out the cable that comes with the dash cam. Thread this around the edge of your windscreen, down past the door, and under the dashboard. Use little adhesive clips to secure the cable. Once that's hidden and reaches the battery, which you can store in that little net pocket in the middle between the driver and passenger's feet, you'll need to connect the battery to the cable. OK, the camera will now record continuously until you flick the top switch on the battery to off. If you forget to do this, the dash cam will continue to record for the length of the battery (8 hours) or for the size of your micro SD card.
I keep the dash cam recording even while I'm parked.
When you need to recharge, disconnect the cable from the battery, remove the battery from the net pocket, take it inside and recharge it using a 14V 3amp laptop charger, which you can buy here.