[EricH]

Originally Posted by Chris is me

And what escaped you is that the rule specifies exactly one battery. Not "up to one" or just "one" but "exactly one".

What escaped YOU was the text at the top of the rule:

The following items are the only permitted materials for use on the MINIBOTS:

Permitted !=, repeat, != required. If you were required to use the FTC battery, regardless of whether or not the rest of your minibot had any electronics whatsoever (for example, a rubber-band-powered one with a release tripped by the hostbot), then I would lose all respect for the GDC.