A lot of the battery case is empty air, so it would be possible to make something even more compact.
We might also look at making the shell of the mesh extender so that it can physically attach to a battery pack for simple one-piece operation when required, but still allow replacement with an external battery pack.
The battery pack is about the size of a Galaxy S2 phone, but 20mm thick. As mentioned, this could be shrunk with a better battery pack than this cheap one we bought off deal extreme.
We have since refined the prototype further, and found a smaller battery.