Great unit. I love mine, but it's tough to power.
A single Tekkeon will get you 3 - 3.5 hours, as confirm by gakidis an others. If I need to roll for 3+ hours then I'm using the extender pack. That's good for 6+ hour which is perfectly reasonable for anything but all-day festivals.
I also like the Bixnet MP100-12V
. I can't remember exactly how long it powers the ad2k, but it's definitely longer than a double tekkeon. This is a pretty decent battery as long as the output cable is secure.
If you needed to go all day then it's probably best to have 2-3x of anything above or maybe even the monster Bixnet BP160
. That would probably make it through a full day of festival taping, I think.