USPCC rules
OK, I just checked the USPCC website and the USPCC Forum. The website has 1/12th scale listed as 4 cells (just as on the flyer). The latest update on the Forum (4.9.05) states that 6 cells will be allowed. It looks like the most current information is that 6 cells are allowed.
If that's the case you will have to run a 6 cell car to be competetive (especially in stock)