Here is our current battery mount -
http://picasaweb.google.com/Falcon.M...96037253971554
There will be a upper frame on it, we will have a swinging arm that will latch down on the battery with a bicycle quick release clamp that are use on some bikes. Works Great, and BTW that is fiberglass, not metal.
We put it as low as we could go, it is off to the rear of the robot but the weight of the compressor is on the opposite end. Distributing the weight evenly will be vital to a good omnidirectional drive system.