Originally Posted by
You want to go where?
it does not follow that they will then allow any battery of a similar size.
Sorry, I wasn't being very clear. I was interested in whether 'hazmat rules' meant that passenger airlines were not allowed to carry car batteries ... or whether it was 'choice' that they made (that is, they could but it's too much risk/paperwork).
Probably answering my own question, a quick 'Google'
has found this page (which probably applies to planes regulated by the FAA only):
Carriers must transport battery-powered wheelchairs, except where cargo compartment size or aircraft airworthiness considerations do not permit doing so.