[coldabert]

12 batteries is too many unless your robot drains an entire battery per 2 minute game.
Last year, our team could easily get 2 matches from a battery. However, in the final rounds, we used the freshest ones straight off the charger.
The most important advice I can give is to bring more than one charger and always have the batteries charging. Also, be sure to check the voltage of the batteries while their under a load, so that the high voltage from the charger wont confuse you.