John:
Answering for Bruce here, I'm sure he'll correct me if wrong, but a lot of guys are using this:

You'll be amazed at all the uses for this. Charges off USB. I use it to charge all my other devices & power air pumps, etc.
I have the 1000 Watt model, its already paid for itself. Quality product, ~$100/1000 Watt. I've seen similar packagung with other makers labels (
Rayovac is one I just bought at work).
Noco may be the original maker, not sure. It lives in my saddle bag.
CHEERS.
~GiG~