ORIGINAL: Lars from Norway
I came to think of saddle pack here, what about chopping off the ''bridge'' that surrounds the battery and make some custom mounts on each side? Like a plate bolted to the chassi to place them on?
You actually wouldn't have to do any cutting to remove those extensions that hold the "L" shaped holders. They are screwed to the main chassis from the inside(you don't need to open up the chassis if you use a long screwdriver). That would leave two neat pre-drilled holes for attaching the custom battery mounts you speak of.