Jack just finished building up the robots for the Abu Dhabi Science Festival in October. We've made a couple of recent changes; adding a table tennis ball as a coaster on the front, and cutting out some fluorescent vinyl stickers that should look good under the UV light in the arena they are constructing for us.
The only other change was removing the 3xAA battery pack and swapping it with an 18650 rechargeable lithium cell. I had done a quick calculation and worked out that we would probably go through 1000 or so AA cells over the course of the festival. It was originally intended as a cost saving exercise but ended up having some other benefits as well. Although the lithium cell is only 3.7V, it has a much more stable discharge curve than the AA cells and performs considerably better under load, meaning that the robots have better performance, and are also more consistent from unit to unit which makes competition play more fair.