It happened to me as well with a TB48 65% charged, i will test with a fully charged one, before the update I never got the message, and none of the motors seem to be hot, please let's keep us informed if it's really some issue with the update...
Macho man why do you want to put a firewall? what kind of unwanted surprises could happen? Could you clarify that a little more? I'm a junior pilot and I'm getting a little scared.