Capacity Loss on 2011-2012 LEAFs

[vegastar]

I usually check the charge stop e-mail to check if the pack is more than 30 minutes floating.

[tbleakne]

The NREL report posted by Weatherman in the "Expected . . loss 70%" thread is very interesting reading. I know the specific Li chemistry is important, but they mention Li-MnO4 on their 8th slide. I believe the effects they discuss are the same for us, possibly with different magnitudes. They rate the shelf-life loss mechanism, proportional to t^.5, as well-understood, but the cycle loss mechanisms are less well-understood.

In an attempt to measure the relative contribution of shelf-live loss and cycle usage for us, I setup a very simple model comparison between my own data and that of 91040 (Allen), assuming he, being at a similar altitude in the Los Angeles basin, has a similar micro-climate.
S = shelf-life loss in % per year
C = cycle loss in % per 1K miles
His data is for 13 months, mine for 12 months, close enough to ignore the t^.5 dependence for the shelf life.
91040 total loss:
1.08S + 24C = 7.5%

my total loss
1.0S + 11C = 3.9%

Solving above system of 2 linear equations in 2 unknowns, we obtain:
S = .9 % loss per year
C = .27% loss per 1K miles (1% loss per 3.7K miles)

The system is nearly singular, so these results are somewhat suspect. The shelf-life component is very likely larger. 91040's usage rating probably should be higher than his mileage alone indicates because he frequently takes his battery down to LB and below. The t^.5 dependence means we can expect the shelf-life component to be less in the coming year, but this result does not bode well for the predicted total loss.

[Stoaty]

Solving above system of 2 linear equations in 2 unknowns, we obtain:
S = .9 % loss per year
C = .27% loss per 1K miles (1% loss per 3.7K miles)

Interesting, but over 6,500 miles and 8 months I lost only 3 Gids (for 80% charge, rarely charge to 100%). That is 3/224 = 1.3%. Using your formula, I would expect a 2.75% loss. I lost 3 Gids over 5 months for 100% charge (haven't charged to 100% for 3 months so can't give an exact amount of loss for 8 months). That is 3/272 = 1.1%. If linear and extrapolated to 8 months that would be 1.8%. Either way, I think the loss per 1,000 miles is too high. My guess is that the calendar life losses (as a function of temperature) are significantly more than the cycling losses, unless you live in a very cool climate.

[abasile]

Solving above system of 2 linear equations in 2 unknowns, we obtain:
S = .9 % loss per year
C = .27% loss per 1K miles (1% loss per 3.7K miles)

Interesting, but over 6,500 miles and 8 months I lost only 3 Gids (for 80% charge, rarely charge to 100%). That is 3/224 = 1.3%. Using your formula, I would expect a 2.75% loss. I lost 3 Gids over 5 months for 100% charge (haven't charged to 100% for 3 months so can't give an exact amount of loss for 8 months). That is 3/272 = 1.1%. If linear and extrapolated to 8 months that would be 1.8%. Either way, I think the loss per 1,000 miles is too high. My guess is that the calendar life losses (as a function of temperature) are significantly more than the cycling losses, unless you live in a very cool climate.

You do cycle your pack much more gently, avoiding high/low SOC extremes, than 91040.

Also, at 15K miles, our LEAF reported 280 gids (as I've posted elsewhere). At this point, at least with a pack that isn't cycled too deeply, I think temperature effects really tend to dominate. While this is bad news in hot climates, it could be very, very good news for many LEAF drivers in relatively cool areas like mine; their packs might last much longer than initially expected.

[Stoaty]

You do cycle your pack much more gently, avoiding high/low SOC extremes, than 91040.

Do you cycle your pack gently? I understand you still have outstanding number of Gids... of course, that cool mountain living probably isn't hurting your battery capacity any.

[abasile]

You do cycle your pack much more gently, avoiding high/low SOC extremes, than 91040.

Do you cycle your pack gently? I understand you still have outstanding number of Gids... of course, that cool mountain living probably isn't hurting your battery capacity any.

During Year 1, we were relatively gentle in terms of cycling. However, these days we're often cycling between 80% and LBW, as the car is going down the hill (where it's hotter) much more frequently. Year 2 will not be as gentle. We'll see what effect that has.

[surfingslovak]

The NREL report posted by Weatherman in the "Expected . . loss 70%" thread is very interesting reading. I know the specific Li chemistry is important, but they mention Li-MnO4 on their 8th slide. I believe the effects they discuss are the same for us, possibly with different magnitudes. They rate the shelf-life loss mechanism, proportional to t^.5, as well-understood, but the cycle loss mechanisms are less well-understood.

Tom, interesting model, very neat. That said, and I'm sure you are aware of that, it's difficult to make any projections based on two vehicles. I won't have much time this week to revisit the discussion, but I collected all the data that has been posted recently, and tried to correlate Gids to various parameters. I could be wrong, but I saw a small correlation between Gids and car mileage (correlation factor of 2.5%). Surprisingly, seems to be a much weaker relationship to vehicle age (correlation factor of -0.5%). This is likely because most of the cars were about one year old, and none of them have seen less than six months of use. Although I counted more than 10 times as many cars, it was still a very small sample.

[Herm]

However, these days we're often cycling between 80% and LBW, as the car is going down the hill (where it's hotter) much more frequently.

That is still a fairly gentle treatment of the battery. LBW is at the 8.5% SOC point?

[surfingslovak]

That is still a fairly gentle treatment of the battery. LBW is at the 8.5% SOC point?

Herm, it's between 17 and 18%, and well ahead of the knee on the discharge curve.

[Cheezmo]

I just measured my GIDs for the first time last night after a 100% (timer override, starting near 80%) charge.

Delivery late March 2012, Plano, TX. ~2500 miles. Mostly charge to 80%. Have QC'd 4 times in one day, 2 times on a couple of days.

265

Will take some 80% and other measurements over the next few days.