Yes, they are chinese cells.
The 5s 4500mah pack is the same overall dimensions as the FP.
http://www.rc-monster.com/proddetail...3150sp255s4500
I have 2s, 3s, 4s and 5s 5000mah and 4s 6000mah packs in the same length as well(some have been tested a few times, but easy enough to get more). :)