I have seen a few of these threads pop up, and don't often see anyone mention the mobius camera. £44 , loop recording, pretty good low light and the option to begin/end recording when it sees power. Personally for me, two of these and cheap USB chargers would be the way to go.
I have been using a Mobius on my FPV RC Planes, Motorcycle Helmet, Car dash cam and so far they have been faultless.