Thought some may be interested in a simple way to put together a charger for the shop or field. This took about an hour and not much money. You can be as creative as you want but maybe this could be a start for you. This setup lets you switch from power supply plugged into an AC outlet to off to 12 volt DC hobby battery. It gives you a place to store your node adapters and power cord when at the field. I also added a voltwatch to the 12v battery. The only thing I have to add is a fuse and a charing port for the 12v battery. I velcro'ed the charger on so it could be removed if needed.

Requires:

120vac/12vdc 5 amp power supply. (Ebay for <$15 shipped)
Radio shack switch $4
Radio Shack jacks $2
Battery $20
Charger of your choice
The rest is optional. It is an enjoyable small project. Enjoy!