Have them buy all the parts, bring them to you, and do all the work while you direct, and explain that this will cover your butt and you will have to charge them more because it will take much longer since they "helped".
OR - Sell it as a non-moving piece of art and the waiver would state the unit must never be moved under power as this could result in serious injury. Unrelated witnesses, notary, multiple copies, stored in separate locations.
Battery is still a potential risk. Sell the sculpture with no battery, but connections and mounts for the one the customer chooses to buy and install himself. I would give no advice whatsoever other than basic specs required, they pick and pay for it on their own.
You can safely sell a gun that is not safe to fire, or a car that is not safe to drive. In both cases, there is extensive paperwork that states the item is something other than what it appears to be, parts, scrap metal, wall hanging, etc., and that it is NOT to be used as it's original intended form.
Standard waivers are largely useless as you can't predict the future, there is no informed consent.
You could form a corporation, it is fairly cheap but you need to insulate yourself carefully, and since you are personally assembling it, liability still applies.
You could purchase liability insurance, better, get some information on exactly what would significantly reduce the premium, while also get an idea on the size of the rathole you are thinking of jumping into.
