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Battery Condition

TomServo

Active Member
Apr 10, 2014
1,134
683
Belleville IL
My Y is 7+ months old and has 36xx miles on it, this past weekend to use up some of my FREE referral miles before they expired I took a road trip to a nearby Supercharger and decided to charge to 100% (second time since new). Here are the results:
nKSgM4T.jpg

40% and 80%. I usually keep it plugged in but since we have a Volt that shares our EVSE there have been times when our Tesla has gone days with out being plugged in.
 
Oct 3, 2020
154
176
Seattle
You are correct, but a decrease in miles/range, over time (30-40k miles), would indicate a decrease in the battery condition.

Sure, I don’t think anyone is questioning that.

The problem is that all of these similar battery degradation threads are not talking about actual miles driven and are instead making a big assumption that’s based on a range estimate/calculation.

All of this is due to a lack of familiarity with how any EV will behave, which tends to turn into questions/concerns since the natural thing to do is compare it to ICE. The fact of the matter is that comparing an ICE to an EV in terms of energy usage is always going to involve opposite ends of the efficiency spectrum. This difference in efficiency is represented by the fluctuations in range, with the EV experiencing the largest range fluctuations due to its high efficiency and limited energy density. An ICE does not experience this due to the high energy density of gasoline/diesel, while also being so inefficient that losing a little energy, similar to what an EV experiences in the winter, isn’t really noticed...

After owning my i3 for 4 years, I’ve come to understand that the 25% range drop during the winter months is nothing to worry about and temporary while outdoor temps are cold enough.. if I compared that result to an ICE, I would definitely think something is wrong.
 
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jcanoe

Active Member
Oct 2, 2020
1,579
1,602
Maryland
When I drove a 2017 Chevy Volt the winter EV driving range loss due to temperature was easily 25%. The Volt's EV range was best in April or May. I imagine this is also true for the Tesla Model Y. In the Volt it was easy to gauge when winter was starting to return as 65+ mile estimated range quickly dropped to 54 miles, then continued to fall to perhaps 42 miles. This included preconditioning while plugged in for 10 or 20 minutes and using the Volt's heated seats and steering wheel while driving. Prolonged use of the electric heat would further lower the Volt's EV driving range.
 

TomServo

Active Member
Apr 10, 2014
1,134
683
Belleville IL
I apologize, I should have been MORE CLEAR, this question wasn't about battery degradation, but rather the battery pack cell balancing. To be honest I don't even know if that's a real thing or a UNICORN. When brand new the highest MILES displayed at 100% was 309 miles. So now after 7+ months and 36xx miles after a full charge to 100%, the car reported my range as 311 miles, and after draining the battery to 1% and charging it back up to 80% If I slide the slider up to 100% the car reports 312 miles. Again I know it's a number, but it was reporting 309 when new.

I was also trying to determine if I actually got the range increase (from 316 to 326) many claimed happened back in Sept with an OTA update.
 
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mark95476

Member
Jun 21, 2020
918
484
Bay Area CA
That's a very good sign for other owners.

309 --> 311/312 miles, even in the middle of winter!

I apologize, I should have been MORE CLEAR, this question wasn't about battery degradation, but rather the battery pack cell balancing. To be honest I don't even know if that's a real thing or a UNICORN. When brand new the highest MILES displayed at 100% was 309 miles. So now after 7+ months and 36xx miles after a full charge to 100%, the car reported my range as 311 miles, and after draining the battery to 1% and charging it back up to 80% If I slide the slider up to 100% the car reports 312 miles. Again I know it's a number, but it was reporting 309 when new.

I was also trying to determine if I actually got the range increase (from 316 to 326) many claimed happened back in Sept with an OTA update.
 
Oct 3, 2020
154
176
Seattle
I don't believe it has to do with cell balancing either, which is most definitely a thing. After enough time and miles driven, the cells will eventually require some amount of balancing, which is important when you consider how the charge will be stopped when any one set of cells reaches its maximum voltage. This could equate to a noticeable chunk of missing capacity since the majority of the pack could have cells that are not at their maximum voltage.

Pro tip, for the best balancing performance/results, you should use the 'top balancing' technique, which involves using a high State of Charge as close to 100% as you feel comfortable. The truth is that little balancing can occur between 80% and 20% SoC because the cell voltages are so flat throughout this voltage range that there is little voltage difference between cells which doesn't promote balancing. Bottom balancing is another technique, but more care must be taken with this approach.

Having said all of that, in my opinion, the drop in range is purely related to how an EV responds to cold weather.
 
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Oct 3, 2020
154
176
Seattle
Yes, cell balancing does occur at all SoC. I'm very familiar with that thread and completely agree with it. However, the balancing performance/results are reduced when attempting to balance a lithium battery that's not at a high or low state of charge. This applies to all lithium batteries.
 
Oct 3, 2020
154
176
Seattle
Could OP's results be because part of the "reserve" segment of battery kWh is released by the over time?

This would be the 'top buffer' and 'bottom buffer' in the BMS world, which is the reserved energy at full and empty states of charge that's designed/intended to protect the battery from the most harmful states of charge that involve the highest rates of cell degradation. The amount of energy stored in these buffers remains the same throughout the life of the pack from my understanding. Reducing their size is a very risky decision for the long term health of the pack and provides little in return, which is why I cannot see that happening.
 
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