When I left my office last Thursday afternoon my Model S had cold-soaked all day outside at 46°F. After about 5 minutes of driving an alert came on stating "Battery is heating" and energy use leapt to the top of the display while projected range plummeted to 70 miles, down in heartbeat from 210 a few seconds before.
I took this to mean that the car had switched on a powerful heater within the battery system to warm it quickly to optimum temperature. (It did occur to me at the moment that this ambiguous message might mean the battery was over-heating, i.e., thermal runaway in some of the cells; but I considered this unlikely because of the liquid cooling). After another 5 minutes the warning disappeared and all seemed normal.
The next morning as I drove to my office there was an alert below my speedometer that said "12 volt battery needs service"; so I immediately emailed our Austin Service Manager. He got back to me right away, and said he'd have Tesla run a remote diagnostic on my car. In the mean time, he was able to reshuffle his own schedule for the day in order to make time to check my car that afternoon.
When he arrived he wasn't optimistic because the Tesla remote diagnostic had suggested that my main 10wk onboard charger was faulty, and he didn't have a spare. Hoping against hope that the 12 volt battery might be the culprit, he took the entire frunk area apart in my garage to replace that battery which is buried deep and to the passenger side of that recess in the frunk covered by the cargo net. Sadly, no dice - replacing the 12v battery didn't fix the problem.
Kudos to my Service Manager who did his best to solve the problem on the spot.
Now the next step is to have a new 10kw charger FedEx'd from Fremont, not to arrive until Monday or Tuesday at the earliest. In the mean time, my brand new $100K car can do nothing more than look pretty in the garage. Sigh!
I must confess that my previously rock-solid confidence in my Model S has been rattled by this unfortunate event. What if this had happened while I was in Houston, 170 miles from home? Or in the middle of nowhere?
Why would such an vital piece of solid state electronics crap out with only 400 miles on it? At this point we don't know if it failed because of some defect within the charger itself; or whether something else in the electrical system is defective and perhaps overloaded the 10kw charger causing it to fail. Could that "Battery is heating" message the night before have anything to do with this? Can individual modules within the main battery short out, overheat, and thus produce an overload failure in the charger?
It will be quite a while before any of us learn hard details about how Tesla manages 12v and high voltage power because the inner workings of this car are doubtless Tesla's most closely guarded proprietary secrets; yet we can be certain they're burning lots of midnight oil at Tesla as they strive for their ultimate goal of "The Best Car in the World."
I've got my fingers crossed that my replacement charger will solve the problem for good, and that my Model S will now give me at least 50,000 miles of trouble-free driving as I've enjoyed from my Lexus.
"Keepin' the faith."