This might well look confusing, which is because I am completely confused myself.
I bought 2 C5s about a year ago, one with the 12-5v converter, which is fitted on the bike, the other fitted to my helmet using a 5v power pack. Both worked OK after fitting, for a while.
The helmet one stopped recording after about 4 months. The DVR would power up, but the camera wasn't recognised. Rather than go through the agro of a warranty claim, I just bought another one, which appeared to work. That was in Feb/March time.
I've checked the footage recently, and all I have on both cameras are sporadic recordings of between a few seconds and 15 minutes (the DVRs are set to record 5 minute chunks, so go figure that one).
I am sitting here now with the helmet camera and both DVRs, to see what is going on, and I can't get either of them to power up, either with a 5v power block or a wall powered USB supply.