Three days ago my 2016 Model X, ~35K miles, no previous problems, was, in the words of the service tech who remotely checked the instrumentation, "a brick." Would not start, would not unlock, nada. Tried both fobs and phone app. Dead. Called Tampa Service Center (we live in Sarasota, about 55 miles away). Took approximately 15 minutes to get tech on phone. After remotely examining/monitoring, said no obvious cause. Original 12v battery looked OK, 70 % charge on main battery. I had received no warnings of low battery. So flatbed was called and car taken to SC. Next day, got a call that they could detect nothing that would cause the problem, but surmised it could only be the 12v battery, which they would replace.
Yesterday was advised that the battery was replaced and all was fine. Problem was apparently in the low voltage warning circuit which was also replaced/repaired. Early this afternoon they sent a Lyft to my home to drive me to the SC. Lyft arrived at the exact time I requested and an hour later I had my Model X, washed, vacuumed, new 12v battery.
Was given invoice for total service, including Lyft: $0.00.
Doesn't get better than that! :-)
NOTE: We also have a 2018 Model 3, but my wife is temporarily unable to drive due to a medical problem, otherwise Lyft would not have been necessary.
SO: THANKS, TESLA! KUDOS! WELL DONE!