[MetalMan]

Like coolhand said, hook them in series. That way if one of the battery sets goes lower in voltage, then it will trigger the stuttering or whatever the LiSaver does when the low voltage cutoff is hit. If you put them in parallel, then the LiSavers would only be effective if both were making the throttle stutter at the same time - this could be bad if one battery has a slightly lower capacity than the other.