will 2 of these be ok on the system

7.4v Li-Ion Battery - 5200Mah ( 4 cell ) Square Pack

They will sure as heck do the job as that gives you 10,400 Mah of capacity.

Now allow for the fact that you shoulkd never ever use more than 85% of any battery packs capacity and that gives you a safe 8000 MaH.

Now for some maths. I assume your using this in an airplane somewhere between 50cc and 100cc. If you using it on a bigger model then the power expander is a tad small. But assume a 100cc.

My testing on 35% planes using 4 aileron, 2 rudder and 2 elevator show a normal 15 minute flight uses about 250 to 300 MaH. Lets say your a 3D control surface wacker and you use 500 MaH at the very worst case.

You have 16 super safe flights in those packs and reality says your likely to have 20 plus flights on fully charged packs.

You could save some weight and some dollars if you fitted two cell packs as you will get the same result.

Your safe to go for sure what ever way you choose to go.

test

The only limiting factor with the 'sport' is the regulator. Should not be a factor with 100cc or less.