What model are you using?
Pilot Electronics, $40 at Walmart...
http://www.walmart.com/ip/Pilot-Automotive-Dash-Cam/38043040
Wanted to see if it was worth owning one before spending too much money. Honestly, this cheapo one does a good enough job that I haven't felt the need to replace it; and considering it sits in an open Jeep for much of the year, if it gets stolen I won't be out as much money as if I had a Go-Pro! I did put a much larger miroSD card in it (32GB) which is good for about 8 hours of recording. It records in short, 3-minute segments but that's actually better because it makes it easier to determine where something is on the card later on (they are time stamped). With the larger SD card, I can video at 1080p; but the battery doesn't last too long on it so I keep the power cable on all the time. Given that my Jeep has a source tied to the ignition, it comes one when I start it and goes off after I shut it down. Easy-peasy!
Cheers! M2