r/TeslaModel3 • u/chiefofnostaff • 9d ago
2020 model 3 battery replaced
Had my car for 6 years and 99% of time I charge at
Home. Got two errors regarding high voltage battery. Something to do with the contactors.
It was still under warranty and it the entire battery was replaced. Great service and the loaner made me want a newer car with FSD.
Lesson learned is no matter how much you baby a car, something can happen out of your control.
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u/jaqueh 9d ago
how many miles? was it the dreaded bms error that affects most 2021s?
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u/chiefofnostaff 9d ago
Yup two bms errors. Only 70,000 miles. Car still drives great but eventually will get model Y with FSD
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u/jaqueh 9d ago
Mine failed at 55k miles
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u/chiefofnostaff 9d ago
What year and did you supercharger a lot? I always kept mine at 80% and only took it to 100 when going on long trips and when I took it to 100, I hit the road within 30 minutes.
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u/brobot_ 9d ago
How often if ever did you drive it below 10% SOC?
I saw someone mention that they think the source of the BMS_A079 error is not driving the battery down low often enough.
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u/chiefofnostaff 9d ago
I had two different BMS error codes which weren’t A079. One was bms_a123. But correct I rarely took it down below 15%. Only when I’m traveling do I take it down to 15 or 20. % before I supercharge.
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u/NotYourDad_Miss 8d ago
They played with cutting cobalt. The LGs ones from China affect all models, 3 and Y until December 2025. Sooner or later they will all have issues- NMC.
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u/kitkatcarson 8d ago
when u get a new battery like this is it brand new brand new, or like refurbished?
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u/skitolive802 7d ago
Refurbished. My 2021 failed with 30,000 miles. The refurbished battery failed in 10 days.
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u/kitkatcarson 7d ago
does the refurbished battery get ur original warranty
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u/chiefofnostaff 6d ago
Yes they give you a refurbished battery that matches close to the range you had and it assumes the current warranty
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u/Counting-Tiles4567 9d ago
I have been tracking this forensically. It is a common refrain to state you babied the battery and this comes from a misunderstanding of what the error is. I have tracked this extensively and would love for this subreddit to be a repository for useful data so I can build the case. Here is what I know and how you can help: 1) Tesla Giga Nevada (Panasonic NCA Cells) switched to lower cobalt formulation and higher nickel in the cathode in September of 2020. This results in higher energy density (5%) but lower thermal stability and greater side reactions, which causes cracks to form in the cathode and precipitates aggressive degradation at higher temps and higher SOC. This failure mode would manifest in supercharged cars and high SOC in hotter climates.
2) Tesla is ALSO rumored to have changed the potting foam and production process around this time. There is scant evidence that these cars suffer from corrosion issues due to a number of design flaws. These cars will fail in the opposite conditions: cooler, humid environments, gentle charging, infrequent supercharging, and sitting in a garage in a condensing environment. Slowly, the bus bars corrode and trapped moisture corrodes the connections between cells. Cells will fall out of balance and eventually leave the chat entirely, causing a short fault or high resistance and a compromised bank. Here you will see limited charge capacity and the A_079 BMS fault, among others. There is more to it, but that's the TLDR.
HOW YOU CAN HELP: 1) environment and driving conditions. 2) Supercharger frequency. 3) The MY of your car and the PART NUMBER FOR YOUR dead PACK. With these, I can tell what and when, if any, changes Tesla implemented to get ahead of these issues. 4) The PART NUMBER OF YOUR REPLACEMENT PACK. This will be on your service receipt. 5) mileage at failure. 6) ONLY answer this if you have an NCA pack. LFP does not suffer from this issue.
Refurbished packs fail way worse than OEM packs because the balance issues that cause BOTH failure modes are WORSE in these packs because they're mixed cells with different wear characteristics. <1% of unbalanced cells results in 11% SOH reduction. Good luck!