8% degradation after 9k miles, wtf?

[Chewy986]

Hello everyone!

So, I read a lot about proper battery maintenance (or so I thought), but I’m sitting on 8% degradation after 5 months and 9k miles… which sounds like way higher than most people experience and is pretty worrisome.

I charge my battery to 80% everyday as soon as I get home from work. I drive about 80 miles round trip and use around 30% of the battery daily, so when I get home it’s around 50%. I have never charged it above 85% and have been down to 17% only once and very briefly. I charge with my 220v 50a garage plug. I have never supercharged.

Based on the above fact pattern I expected to be in really good shape, yet my results are so far sub par.

I did buy the acceleration boost but mostly drive on the highway and rarely use it. I typically cruise 70-80mph which may be part or the problem. I live in Houston which is a hot climate for the battery and I generally have the AC on pretty high. I suppose the hot environment mixed with AC load and 80mph cruising speed is a bit taxing but I haven’t heard much discussion on it.

Any advice on how I might curb this degradation? Did I get a lemon?

Today I read 57% battery yielding 170miles for a 298mi capacity (or about 8.5% degradation vs new). I drive a model Y LR which is quoted at 326mi new)

 

[Candleflame]

The display in the car does NOT show battery degradation. The only way to truly get an accurate number is to charge the car to 100 percent and drive it until it is dead and measure the kwh used. That is the only way.

that is simply not true for 2 reasons:

- the BMS is extremely accurate except for fringe cases
- The BMS does not let you extract more energy than it thinks it has available. So essentially while a deep discharge may recalibrate the BMS a little bit after a few weeks/months you will not see the fruits of this action immediately

Might add here that self proclaimed youtube experts i.e. bjorn, that american guy etc have never managed to get more kwh out of the system than the BMS tells you. For reason mentioned above. (+-1%)

 

[Seminole]

I’m right around 10k. I was seeing lower estimates around 300 so I’ve tried to do some BMS recalibration by doing deep discharges and charging back to 90% and letting it sit at various states in between. I’m around 310-311 now.

I also plugged my car back into the scan my Tesla app for the first time since I got it and it looks like the nominal full pack has gone down about 4.7kwh which would be 6% degradation. I assume that’s a real number and the BMS calibration would have nothing to do with that.

 

[AAKEE]

I’m right around 10k. I was seeing lower estimates around 300 so I’ve tried to do some BMS recalibration by doing deep discharges and charging back to 90% and letting it sit at various states in between. I’m around 310-311 now.

I also plugged my car back into the scan my Tesla app for the first time since I got it and it looks like the nominal full pack has gone down about 4.7kwh which would be 6% degradation. I assume that’s a real number and the BMS calibration would have nothing to do with that.

Nonimal full pack is the source to range on the screen. The range is calculated by dividing nominal full pack by the charge constant.
The charge constant is 240-242Wh/mile 79100Wh / 327mi = 242Wh/mi (first picture)
74400/310 = 240Wh/mile. (recent picture)

I have the same battery and my NFP have shown a solid 80.4 to 81 for the last six months. I understand that my charging schedule offset the BMS slightly to overestimate the nominal full pack value. A regular BMS calibration do not fix this, I have performed two resets by discharging the battery well below 0% (about -2%) and let it sleep there. When doing this my NFP went down to 79.5kWh both times wich is very close to my own estimation about what capacity my battery should have.
Back to using the regular charge schedule the nominal full pack climb back to the 80.5-81kWh value.

I guess this means for you that the BMS calibration value of range/ NFP probably go back to about the value you had earlier( ~300 miles) after some weeks.
6% is probably not far from the real value as the calib should have set your BMS on track.

I do not know your cars age but I would say that after about one year with the car standing a lot at 70-80% SOC and a medium climate you would have in the ball park of 6% degradation.

I have more or less the same BMS value shown as when the car was new( 80.6 New and 80.4-81 without BMS calibration).
I had the NFP showing 81.6 a few months after the car was new with 82.0 nominal remaining so I recon my battery actually had 82.1kWh capacity when it was new.

82.1 kWh reduced with about 3% degradation according to my own calculations set the capacity at about 79.5kWh which is perfect in line with 79.5kWh NFP.
(16 months, 40.000km/25.000mi)

 

[Sage Brush]

Thanks OP for the updates. Great thread!