This should be a quick and easy question.

Is it legal to build one's own custom circuitry to charge the backup battery from the main 12v battery system during the competition? FIRST distributes a rudimentary charging system schematic, but my specific question is whether or not it is legal to charge the backup battery during competition with a custom-designed battery charger.

Any insight into this issue would be greatly appreciated. I know that many teams are having difficulty with the longevity of the battery life of the backup battery. This should be one way to help out. If it is determined that it is legal, and our if team can get our design to work, I will be sure to try to post the schematics on this thread.