Battery
 

Would a battery for powering decorations be allowed? I don't think so, but can anyone confirm this?

In the case you are describing(a non-functional decoration,) an auxiliary battery would be allowed. Non-functional decorations are not restricted by the other rules regarding what can or cannot be used on the robot. It would still count against your weight limit, however. It is allowed for your decorations to draw from your 12v battery already on the machine, so if this is an option in your case, you may want to consider it...