Yeah, good point. IATA has some guidance (https://www.iata.org/contentassets/05e6d8742b0047259bf3a700bc9d42b9/lithium-battery-guidance-document.pdf) and so does UPS for shipping separately. Basically none as cargo on a passenger plane.
For a previous job I had to install some big battery supported power supplies. Shipping of the batteries was a pain, but ultimately there's a process, we followed it and the batteries arrived. They had to come by sea, so a long lead time.