www.boxertrix.com

Are there really people out there of sane mind who are prepared to pay such a ridiculous amount of money for a motorcycle battery?

https://www.ebay.co.uk/itm/BMW-R1100S-1 ... Sw905ZykiW

Is that even close? Or is it a method of preventing purchases when you no longer have stock?

(I admit - the odd amount, seems at odds with that theory)

lithium are that sort of price

Yep, I've put a Shorai on my Ducati to prevent any damage to the sprag clutch on the starter motor (if it kicks back, they can strip). However, Lithium batteries need treating differently to Lead Acid types, and give a useful boost in cranking Amps, despite this, I think making some thicker battery and starter cabled the most. Be careful about buying Lithium batteries, the better ones have a built in balancing circuit so all the cells charge at the same rate. If they don't, it can lead to a fire - just ask Boeing! The lighting rig I use for Caving has been revolutionised by lightweight Lithium batteries, I can stay underground much longer now without carrying big heavy batteries, or have the problem of keeping Carbide dry.