In Lipo's, 4s1p means this... 4 cells in Series in 1 Parallel wiring or just 4 cells which is 14.8v 4s2p would be 4 cells in Series with 2 in parallel or 8 cells total but would still have 14.8v. however, the amps output would double. So if you have 4s1p at 4000mah with a 4s2p you would have 8000mah.

I hope that makes sense 'cause I just confused myself. Oh, because of the higher amp draw, you may want to get a minumum of 20C rating packs with 3700mah being the lowest mah rating.