I don't think there is much money in it. Typical rack-pack 100AH/48v is 16cells, 105's so, .... next. The other guts are wiring harnesses, front panel displays and a BMC, along with the chassis. Have you priced a 4-5U rack server cabinet for a computer with no power supply or anything in it? $250+? + $100 for the BMC and $50 for the wiring BS, call it $400 for a box at best. So now I spend my $700 on the batteries and $400 on the box, I've got $1100 tied up in a DIY setup, or I could spend the $1350 and just get something already made, perhaps with some kind of support or warranty. It seems rackmount heavy duty steel boxes are not all that cheap.