I fitted an extra battery into the boot of my car, and have it cabled to the car charge circuit.
That way it is always charged, and I never have to worry about starting my car!
It pops out easily for running the gear when I am at a dark site, and I can't forget to take it or forget to charge it
I fitted a connector to it so I don't have to remove it from the car if I can park close enough, but it is easy to remove if required.
If you know what you are doing, you can do it yourself, just make sure you add an isolator, or you can get off-the-shelf kits:
http://www.arb.com.au/products/arb-d...ttery-systems/
http://www.tjm.com.au/index.php?nj=ln.php?i=DBS