You could remove one battery from the engine area, move it to a saddle bag, then add the 2nd saddle bag for 4 total. Or, you could ask me to help out and I could probably take care of that welding for you. I'm no professional, but I can put two pieces of steel together (
some of my work). I doesn't look like it would be hard to extend the very bottom a few more inches for another battery to slide in there.