The 40KWH Battery Topic

I've read a few scientific articles but when I just googled to reference them I realized that many of them are > 5 years old, so probably irrelevant at this point. Li battery technology is changing so fast that anything over few years old is obsolete. For example, the 40kWh and 62kWh Leaf batteries appear to be behaving quite differently than previous batteries. And who knows how 2022 40kWh batteries compare to 2018 40kWh for example? Manufacturers continuously update materials and processes and while major customers are privy to these changes if specified by contract, generic users like someone buying a car will not be. In any case, the trend seems to be our friend here as most reports indicate that the batteries are getting better every year.

Nissan does tend to announce changes in battery chemistry. I'd actually be surprised if they had changed the 40 and 62 kwh batteries since they were introduced.

knightmb said:

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That is one beautiful histogram!

SageBrush said:

rogersleaf said:

DaveinOlyWA said:

You had a positive adjustment Roger. Aint it cool!

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The weird part is I haven't been babying the battery or the car this past Summer. I still use the charge timer, but morning departures have been so irregular lately that it's usually fully topped off to 100% before departing for work. Then it gets quickly run down to @ 75%. Then sits 8 hours before burning another 30% to get home and maybe 15-20% more if running errands. So basically cycling daily using 60%+ of the pack capacity, but that's the top 60%, not the middle 60% (20-80%), it's rarely deep discharged, and almost never DCFC.

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Charging to 100% SoC and leaving the battery to cook at 100% SoC are two very different animals. And if you really want to toast your battery, charge it to 100% SoC when the battery is hot and then let it cook.
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For our LEAF, this might be the first winter that we elect to charge to 100% rather than 80%. Since we don't use scheduled timing in the winter to avoid charging a cold battery, the car is destined to sit at 100% until its next use but at a low battery temperature. We'll see how that behavior affects degradation.

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Usually by the middle of January, I would like to be someplace warm enough to totally cook my battery... but that's a different problem in life.

The past 2 Winters I didn't do much distance commuting due to medical leaves, Covid-related WFH, and an employer that finally got wise to the idea that if the road conditions are bad just stay home and work. This Winter I anticipate getting a better idea of cold stress on this car. If this car behaves anything like my previous '14 LEAF, any major capacity/range drop would likely be magnified in the cold. Last week I even got a set of Michelin X-Ice mounted up on 16" wheels ready to install on the car next month, pretty sure that won't help the range expectations.

rogersleaf said:

If this car behaves anything like my previous '14 LEAF, any major capacity/range drop would likely be magnified in the cold.

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That is why I'm inclined to charge to 100% SoC

LeftieBiker said:

That is one beautiful histogram!

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She doesn't even try either. :shock:
Makes me wonder if I am being over-protective trying to operate mine between 20% and 80% in a casual sense. It's just by utility I don't need to charge to 100% or discharge below 20% all the time, my wife, she never gives it a second thought. Going to visit a friend 10 miles away, better make sure it's 100% before she leaves or else a spontaneous road trip might happen. :lol:
I should have never told her about the hidden capacity after 0% :?

If it works, don't fix it It's always great to see a success story like this since usually folks only post when something is wrong.

LeftieBiker said:

Nissan does tend to announce changes in battery chemistry. I'd actually be surprised if they had changed the 40 and 62 kwh batteries since they were introduced.

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They usually mention "continued improvement" in processes but are literally never specific about anything... By all accounts, the 2022 did change. It drives differently which is the obvious for anyone who had an earlier Gen 2. So what else has changed?

I assumed the majority of changes were due to Nissan reducing the trim levels and options, reducing production costs.

For the battery hopefully improved quality and fewer bad cells.

3 years 7 months, 30K miles, SOH 89.79, Lives in Atlanta. The last 2 three month adjustments were positive.

Mostly charge to 70% no DC charging.

So a 8% drop in first year, then 1-1.5% a year there after.

DougWantsALeaf said:

So a 8% drop in first year, then 1-1.5% a year there after.

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sometimes. I have seen 5ish% the first year, 3ish the 2nd then 1ish after (like Gerry's) but no matter how the first few years look, most seem to merge together within 2% after 3 years or so.

DaveinOlyWA said:

but no matter how the first few years look, most seem to merge together within 2% after 3 years or so.

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Can you rewrite that in English ?

SageBrush said:

DaveinOlyWA said:

but no matter how the first few years look, most seem to merge together within 2% after 3 years or so.

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Can you rewrite that in English ?

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@3 years most are between 89 to 91% SOH

One question I have is whether the BMS is programmed to use up any hidden 'extra' capacity to force the SOH to follow a fixed trajectory or if all the batteries tend towards the mean as they age. Or it could be a combination of both but it's odd how closely the population of batteries seen here is tending towards a fixed SOH trajectory.

goldbrick said:

One question I have is whether the BMS is programmed to use up any hidden 'extra' capacity to force the SOH to follow a fixed trajectory or if all the batteries tend towards the mean as they age. Or it could be a combination of both but it's odd how closely the population of batteries seen here is tending towards a fixed SOH trajectory.

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While that might be a good "conspiracy theory", I think it's just a sign that (after 10+ years) they have finally improved the chemistry and/or manufacturing process.

Even if the BMS was programmed this way I wouldn't assign any malevolent intent to anyone. It may just be a good way to make all cars behave 'the same' as much as possible. Many manufacturing calibrations do exactly this so that the embedded control algorithms are normalized to a common model.

I think we can all agree that we don't really know how the BMS handles SOH or even what it exactly means. There is an obvious 3 month time frame that results in step changes in the reported SOH and also cases where the SOH has increased at these points. To me, this implies the BMS is doing something more than just reporting the status of a continuous, inevitable decline in battery capacity. AFAIK, no one here knows enough about the internal BMS programming to know what exactly it is doing but that's fine with me. I check my SOH about once a year now and that is all the resolution I need.

goldbrick said:

I think we can all agree that we don't really know how the BMS handles SOH or even what it exactly means.

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We know the cell voltages. End of story, +/- some calibration drift

True, but the BMS is managing access to the top end of the pack voltage, no? It feels like the bms has a relatively simple algorithm which limits a bit more aggressively for cars which charge to 100% frequently or DC charge frequently. That said, there does. Not appear to be much of a difference after a couple years. Even the brutalized packs are not much different than the pristinely managed packs from the little we have seen.

Livery cars with crazy high cycles are down a few % more, but that's somewhat to be expected.

goldbrick said:

One question I have is whether the BMS is programmed to use up any hidden 'extra' capacity to force the SOH to follow a fixed trajectory or if all the batteries tend towards the mean as they age. Or it could be a combination of both but it's odd how closely the population of batteries seen here is tending towards a fixed SOH trajectory.

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Doubt if its that simple. Probably just have a better chemistry and better management in play.

I was collecting LS data to delve into the possibility of any emerging trends but the sample size is limited and no definitive patterns have emerged.

The next step is getting LS shots at full charge as it seems the full charge SOC runs between 100.00% (shocking aint it?) to 97.5% to see if there is any pattern there?