I'm with Captain Ron. Building one string not an issue, start building 90-120KWH or more, now you have to deal with multiple busses multiple BMC's and a place to put it all. Once you start buying a standard rack cabinet, and a rack and bus-bars and ... The price differential drops dramatically. I mean if you are willing to go to Costo and get a steel shelf, and shove a few thousand pounds of batteries on it, then run a bunch of busses along the edge and, ... or build something . . . Or just buy a 30KWH rack with a bus and wheels ready to go, cable it up with some 4/0 and fuses. It's the maintenance angle too, I'd rather just shut down 100A a pop and swap it. If you have lot's of room and you like fiddling with lot's of wires, and tweaking BMC's, and custom building racks and mounts for big prismatics and BMC's, then you can save a few bucks, assuming your time is free. Sometimes it's not about the money, sometimes it is.