Just to put things back into context.
Kan Opener squeezes you with battery power.

Both the above statements .....mine and Andys are really irrelevant to the original concern about weight.

All A123 battery testing Robots should.. IMO .. weigh in at the Championships UNDERWEIGHT by some 2 or 3 kgs ...thus proving that they have ONLY replaced their original batteries with a like for like Amp/Hr rating ....thus gaining NO appreciable power advantage and also showing that extras havent been added due to having a couple of extra kilos spare.

Alternatively ....If they really want to be top limit on weight ......A couple of housebricks tapped inside should be OK for ballast