has anyone received this message after the latest software update?
popped up right after the update and won't go away.
message telling me to "replace 12v battery soon"
Sounds like you need a new 12V battery. I believe that they usually proactively replace them at every alternate annual service. I got the warning at over 100000 miles in my Model S. It cost me under $200. But it will be under warrranty for you at this time. If you don’t do it the car will shut down. So call them up and you probabaly need to get it done in a week or two.