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Tesla Stands by its Battery Pack Warranty

Wednesday my beautiful P85 Model S became disabled, requiring a tow to Tesla Service.


But by noon Thursday Tesla restored it.


And therein lies a tale.

On my way back home from a longer-than-usual day trip, thoroughly enjoying the Tesla driving experience, I stopped around 2 pm at a major-chain grocery store a couple miles from home.

After loading goods into the frunk, I returned to the driver's seat, and the double-boop alarm immediately rang coinciding with a written warning saying "Car Needs Service - Please pull over safely". Since the car was still in Park, I thought that was a strange warning.

Then I tried to put the car in Reverse. It refused. Same for Drive. Then a new warning came up: "12V battery low - Car may shut down unexpectedly". That alternated with the first.

I took delivery Feb 23 of last year, it now has about 14.6k miles, and it had its annual service five weeks ago.

I got out, got back in, and started over. Same results. Now I was convinced it would not move again without help.

My next step: call the Tesla roadside assistance number via my cell phone.

After reaching Andrew at Tesla HQ, I described the situation. As we spoke Andrew downloaded the log files. Pretty amazing; it's like the telemetry mission control collects from spacecraft.

In a short time Andrew said "It looks like a problem with the drive inverter". That's pretty serious, since that's how DC is converted to AC to power the AC induction motor. Andrew walks me through shutting down the car then rebooting. Still doesn't fix anything. Later on he says it could be some sort of wiring issue, preventing the main battery from supplying power, explaining the drain on the 12V battery. I could understand diagnosing the car from 400 miles away in a few minutes is not easy.

So Andrew says he's going to call the local Service Center, 12 miles away in Costa Mesa, and schedule a tow truck to come get the car.

At 3 pm the tow truck arrives at my S. I'm fascinated with the process the tow truck driver uses to keep the 12V systems alive (take off the nose cone to access the 12V posts) then hook up the car (it seems like he attached straps to the struts of the front suspension).


At 3:30 pm the Tesla is almost completely secured, so I leave for home using other arrangements.

Late at night, I check on my car using the Tesla app, and discover it is charging at about 25 mph and 200V 39A and I confirm its location at the Service Center. I happened to be up at 5 am and checked again and found charge was complete at 272 miles of range.

That is notable because a couple weeks ago it held a maximum 257 miles of range. 272 miles is what it could hold when new, last year.

Next morning at 8:15 am I call the Costa Mesa Tesla Service Center for my car's status. Brandon of Tesla told me that it was all done. Great news! And we coordinated when that morning and where Tesla would return my car to me.

But I wanted to know: what was wrong and what did they do?

Brandon explained that the car has two "contactors" that allow the battery pack to power the car. He explains they're like really big relays. I surmise those make the "clunk, clunk" sound when one first activates the car.

"We think one contactor got pitted." he says. Later I look it up and it's how relays get stuck:

NAASCO Northeast Corp. - Article

Any electrical arc between the contacts can cause wear and "pitting", increasing the electrical resistance at those damage points. Since I already estimated that the battery probably delivers up to 1000 A, that's a highly concentrated potential heat source, enough to fuse metal.

So the car detected an electrical problem, due to a contactor stuck closed, and entered a safe mode. "So what was the fix?", I asked.

"We replaced the battery pack," he answers.

I'm floored. That explains why the range is 272 miles, just like new, but I'm aware of the estimated cost of a 85 kWh battery pack. The consensus I've read is that it must be at least $25,000, perhaps up to $33,000. That's an enormous cost, but it's also shows their commitment to Elon's bolstered battery warranty, covering virtually anything short of sabotage. I'm impressed that the decision on such a big expense was made so quickly.

Then I ask, "I had my annual service last month, so was there a way to catch this problem then?"

He answers "The contactors are inside the battery pack, so we couldn't look at them in a normal inspection." Since the battery pack is sealed, is electrically non-trivial, and is a structural component, that makes sense to me. One wouldn't risk disturbing the innards of a component so highly critical to the car without a good reason.

So I reiterate to him how impressed I am that they swapped out the entire battery pack. He says they completed that by the end of the day. I encourage them to take the time that morning to check out the car, saying I'd rather they be thorough than rushed. I'm still impressed that in only a few work hours they swapped a 1200-lb component and fully restored a critically disabled car.

Tesla covered the whole expense, and now I have a fresh battery pack!

Interesting observations:

I deduce it takes the Tesla Service Center an hour or so to swap a battery pack, perhaps less. My car probably arrived via tow truck sometime past 4 pm, then they needed time to diagnose it, so we were lucky (!) enough that a brand-new P85-compatible battery pack was on hand, so they worked from maybe 5 to 6 pm to swap it out, then test it, then charge it to full overnight.

The coordination of the Palo Alto headquarters with the Costa Mesa Service center is pretty tight. From experience the Service Center's normal workload is busy enough, but they were able to promptly deal with my car.

I called at about 2:20 pm and the car was returned by 11:30 am the next day. I could've asked for the car earlier in the morning. I appreciate the speed of that turnaround.

I'm lucky this happened just miles from home. I wouldn't want to imagine if this occurred on a distant road trip. Then again a critical failure can occur in a car of any power train.

Unanswered questions:

What's to become of my old battery pack? Even if they replace the stuck contactor, surely they can't simply install it in a new Model S. Who knows if a few of those 7000 Panasonic 18650 batteries have failed.

Does Tesla refurbish battery packs? Perhaps they'll take it apart for study, to learn what happens to a battery pack after 14.6k miles of use. Then maybe they'll reuse its components with that of others to create refurbished battery packs that they use for replacements like in my situation or for the announced Tesla "battery swap" stations. (One of you will have "my" pack!)

How many brand-new battery packs do these Tesla Service Centers keep in stock? They probably need one of each of the 60 kWh and 85 kWh. Perhaps a third for a P85?

My Questions to TMC members:

Have any of you had your battery pack swapped due to a failure (not an upgrade)?

Have any of you exercised the battery pack warranty?
Sounds like it was just the connection part that failed, not the entire battery pack. It's easy to swap out the battery (it's obviously designed to do that). I bet they ship your old pack back to the factory where they open it and fix the connection part and then use it for another battery warranty case. They are not losing the entire pack, it's just easier and quicker to swap the pack when a customer needs his/her car back.
Most service centers keep 1-2 85KWH packs, in their crates ready to go. Service centers swap out the entire pack at a time. Packs consist of all the contactors, BMS, battery modules and cells in those modules etc. The Service Centers don't work on the pack itself at all. They change the entire pack out as a module and ship it back to the factory for repair/refurbished. The reason is that opening up a BEV battery pack requires specialized protection and equipment including arc-flash protection and isolation, insulated tools and other specialized equipment to disassemble, repair and reassemble. David99 your assumption is more than likely correct, this refurbished pack gets shipped back out to any of the other service centers to backfill their inventory on demand, as needed. And the circle of battery pack life continues...
Thanks for posting dauger, nice looking car btw :smile: Just FYI the 85 packs are the same. Difference in the P85 is a higher output inverter and more winds on the motor (one moving part!!) ML

and - A packs can SuperCharge (of course) but are limited to taking 90kW from the charger.
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Slight OT but very interesting. Here is a very interesting guest talk at Standford University by Dave Duff who is a mechanical engineer at Tesla. He designed several things for the Model S including the single connector that connects the battery pack and the car. Back when he gave the talk the battery swap wasn't announced yet so he avoids the subject a little when asked about it :) Anyway, very interesting talk!
Stanford Seminar - Dave Duff, Telsa Motors - YouTube
Have any of you had your battery pack swapped due to a failure (not an upgrade)?

Yes, my car was in for some fixes and while the tech's were updating my firmware they bricked my car. No idea how or why, Fremont called in, couldn't figure it out. Got upgraded to a B battery as a result...unfortunately this happened on a Friday night, and they had to bring in a battery so I didn't have the car for the weekend, but they replaced the battery without question.
Yeah, if only my A pack would fail. Great to hear that Costa Mesa and Brandon got you back up and running so quickly. Although if it were my car I'd gladly let them keep it however long they wished as long as I got a 120 kW capable pack.
Great service experience!

Is the pitting a genuine concern though? Sounds like it could happen to any of our cars. And, a whole battery pack replacement is mighty expensive for Tesla for what is seemingly a small/cheap but single point of failure.

The battery pack is a sealed unit, they determined ultimately that a capacitor failed in my battery, but given how the battery is designed, apparently even a small component failure within the battery will require a full replacement.
It's much safer to replace the pack at the service centers. The pack can then be sent back to the factory for diagnosis and repair. The packs are dangerous and should only be serviced by highly trained and qualified personnel. At this point having people with those skills at every service center is not practical or financially viable.
Exact same thing happened to my sig two weeks ago -- was in another building for a meeting and when I got back to my car it was dead. They managed to start it again by hitting that relay with a rubber mallet and drove it to the service center, which was a good thing seeing as the tow truck could not get into the underground garage. I will be checking my pack rev now actually as this is the first time I have been around since the swap!

Updated after confirming:
Well, they replaced with another Rev A. No wonder I haven't seen any charging improvements.
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And, a whole battery pack replacement is mighty expensive for Tesla for what is seemingly a small/cheap but single point of failure.

Not really. The pack goes back to Tesla and whatever is wrong with it is fixed. It is then shipped back to a SC and will be installed as a warranty replacement on some other car that needs it. By doing it this way Tesla avoids upsetting owners by having their cars in the shop for a long time, and they also have the chance of having engineering inspect the failures and develop improvements. It's a very good way of handling it.
If you consider the Model S as a very large laptop computer with a 17" touchscreen and a battery that can power the laptop for 9 months - then the battery pack service strategy is really not any different than sending a laptop in for service with the manufacturer - when they may replace all or part of the laptop with refurbished parts, and continue to the original warranty (or if out of warrant, provide a short term extension for the replacement parts).

The battery is a very expensive component in the Model S - expensive if you are purchasing a brand new battery pack. But it is made from many (over 7000 batteries) less expensive parts, and most failures (and possibly even battery pack degradation) will likely be confined to a small number of the components - so by replacing them, the battery pack can be refurbished to virtually new condition.

Tesla has previously mentioned having a longer range battery policy - to cover a replacement battery pack - and possibly extend coverage beyond the original 8 year battery warranty period. As they gain more long term experience with the Model S battery packs, hopefully they'll consider offering that using refurbished battery packs - which should have a considerably lower cost than buying a brand new battery pack if/when the original pack degrades significantly (below 70%?).
Thanks for posting your experience. I just had the same thing happen to me - same warnings, diagnosis and excellent service. I'm VIN 646 and have 27K miles. I was told that I received a refurbished battery that should be like new. I wasn't aware of the A, B battery references (I don't go on the forums that much). Where do I find the battery label?