Jerry:I expect that the only thing that changes with the firmware upgrade is the ESS/Aux battery test only runs once. This would not change any other aspect of starting or jump starting, both batteries are still in parallel and each would still have the same impact on starting or jump starting. Except with the old firmware, there is never an attempt to crank the starter if the ESS/Aux fails the test. With the new firmware, it will attempt to crank the starter with a bad ESS/Aux battery.
I too have a portable battery pack I bought a while ago for my previous vehicle and now have a 2021 Unlimited Sahara. The 2021 owners manual does state that a portable battery booster pack will work. Do you think this a new? and something changed?