I assume you mean fput together two 2S lipos? You just need to buy a series connector to connect the two 2S lipos in series - that makes them a 4S equivalent.

They need to be the same mah, same 'C' rating and have about the same charge/discharge history. Before you hook them together, they need to be about the same voltage too. Ideally, you would charge them this way as well (hooked together as a 4S). I've done it both ways and don't see much difference, charging as one or charging separately.


http://www3.towerhobbies.com/cgi-bin...&I=LXYHX5&P=ML