this is how I run mine aswell.
I run the Ua-5 and two Jb3's off of them.
I have (2) 12v7Ah and (4) 12v5Ah I ran the two 7Ah last year at wakarusa for over 20 hours
I got a killer deal on the 5Ah brand new on ebay (all 4 shipped for $15 ) so I picked them up aswell
And the more I thought about it I could power the Jb3 at the campsite by one of them and playback the show from earlier that day while making dinner/lunch at the campsite.. without draining the internals or using needed juice from the 7Ah 's
heres a rough pic of my batt set up.. I used the adapta plugs and they were both black so I got the idea to take some of the My girlfriends red fingernail polish and make a line so it would be almost
stupid proof in the dark at a show. you can kinda see it look at the top of the Jb3 (see the red line) on the adapta plug going into the back of the Jb3, just make sure the red line comes together and were golden..
cables are (2) 10ft mogami and a single 25ft AT cable ,just to show size reference (Thanks to Nick M for the deal on the AT cables )..