With the set up I am using there is a big difference between two and three cells even indoors 2 cells is slow aerobatics nothing fast it has power to hover and pull out pretty good but three cells really gives you that punch you want for really good 3D I even find myself using 3 cells indoors allot but my dad still likes 2 cells on his tensor with the same set up. Another reason I use three cells outdoors is the extra weight my tensor has such a light wing loading that it had to be dead dead calm before I got the thee cell packs (kokam 340's and kokam 640's for more wind and longer flight times)