6600mAh is highest at the moment
but you can put two packs in parallel to get 13200mAh
if you want 11.1v
you need to buy 3 packs of 7.4v 6600mAh
then repack them into 3 cells in series x 2 parallel
then you get 11.1v 13200mAh (I think its 20c)
Why you need something bigger than 6600? That should last a long time already. Rather take a few mintue to change battery than making the car soo heavy. Therefore, 串聯 make sense because the car will be faster, but 並聯 doesn't.