The 18kPV can handle 200A from whatever battery setup you have. So a single battery could be asked to move up to 200A. I'm not exactly sure of the ampacity of the included cable. It's 2/0 AWG with some kind of PVC insulation. (135-195A depending on who you ask. It's really about how much heat the insulation can tolerate, and whether you plan to put it in conduit.) 200A through a single cable might be asking a bit much. Doubling them up would allow them to run much cooler.
If you had 2 batteries though, each could only be asked to move 100A, because of the 18kPV's 200A limit. So only a single cable set from each battery wouldn't be an issue. In the case of the 6500, I'd guess it has a lower amp rating than the 18kPV? I don't know the specs of that one.
