Elegant design notwithstanding, there are some fundamental realities of mounting batteries you have to be aware of.
First, batteries are heavy. And dangerous. Whatever you do, you have to make sure that the batteries are supported adequately. They’re corrosive. They, in the case of lithium, will catch fire under certain circumstances, one of which being if the lithium is exposed to water. Besides that, there’s the obvious- you have them wired together to produce high voltage and high current. This is all fine for normal running, but you also have to consider a design that will be as safe as possible in a collision or accident. What may be fine in a normal upright position may kill you, or an EMT, in the event of an impact.
Individual battery design will dictate how the mount is designed.
Flooded lead acid batteries (in my humble opinion, although a very cheap option, also an incredibly dangerous one) MUST be run in the upright position only. They, of all designs, should be enclosed in some sort of spashproof box, and the design of the boxes should be totally overkill- anticipating the worst accident considerations.
Sealed AGM batteries can be run in almost every position except upside down. See the manufacturer’s specs, but they give you a lot more flexibility in designing an enclosure. They won’t splash or spill, even if the case is cracked open in an impact.
Most lithium batteries, like Thundersky or CALB, can also be run in almost any position except upside down, but they want to be bound pretty tightly. They expand and contract, and the cases aren’t really designed to withstand that stress without support. Many resellers will configure packs for you, with your configuration specs, and strap them accordingly for your safety. This is all good, but you have to know what you’re doing, and what will work in your configuration.
Many lithium batteries are running their outside shell as a positive, or, at least, very close to the positive- as in the Headways. It’s a really bad idea to use a conductive material for holding these things together- a little abrasion and you’re direct to positive of the pack. Keep in mind- carbon fiber, however strong and light, is made of carbon- one of the best conductors on the planet.
I’ve tossed around a few ideas for modular rack systems for mounting the cylindrical Headways- I figure a high strength plastic like Delrin might be the best material to cut them out of- here’s what they look like.
My best advice, though, is to get the batteries in hand before you commit to a mounting system. It’s one thing to toss around theory and design something- it’s quite another to be holding over 100lbs of batteries in your hands, and imagining what would happen in a 50mph crash. In the motor mount chapter I suggest designing only for the minimum stresses. In this case, I don’t think you can overkill the design enough.
Keep all this in mind in your fabrication, too. If you’re not trained in this stuff, don’t have a feel for it, new to welding, or considering a light-weight frame or box structure held together with bolts, or looking at an exotic or untested material, you’d be wise to look to some experienced help- either a motorcycle frame guy or a good builder- and listen carefully to their advice.