The Zeus is not a battey pack, it is a "plug in the wall" A/C flash generator. The small one pumps out 1200 watt seconds and the larger one pumps out 2500 watt seconds. I think what you may really be looking for is the ABR model which is a self contained monolight/ringlight that works very well. I've had one for about a year and find that, since you tend to work very close to your subject with a ringflash, you don't really need more power than the 300WS you get with the monolight unit. It is still A/C powered so you will need to use an outlet or buy one of the Alien Bees Vagabond Battery systems to use the unit on location. I have the new Vagabond II battery pack and find it to be an awesome addition to my lighting kit as it will power my Profoto Acute 600e flash generator and two heads while providing fairly fast recycling times.
Go back to the Alien Bee's Website and search for the ABR. I think that's what you really want.
Best, Kirk Tuck
www.kirktuck.com