lipo's in series and why one would be different in voltage?

[BrianG]

Actually, it probably should go into the General Electric section given the topic.

I wouldn't go by any of BrianG's charts since he doesn't know what he is talking about. j/k.

Anyway, then I would say that either one of the cells is a bit weaker and/or the cutoff is a bit too low. Try increasing the cutoff to 3.2v/cell. I assume you balance the packs when you charge them?