ORIGINAL: piper_chuck
A Y harness would typically put them parallel, which would give you the same voltage output, but double the capacity, but if the polarity is reversed, some wires and batteries might get really hot. A better question is what are you trying to do?
A Y Harness?????
Vernom290, are these to be used with a BEC on your ESC?? Also what was the configuration of the stock battery??
Don