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gbarry42
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Charging from 80% to 100% -- What's the issue?

Thu Aug 04, 2011 2:36 pm

Nissan states that charging to 100% from 80% (or above) is not good for the battery. While I can think of things that may happen near a full charge, 80% doesn't sound to me like it's "that close" to a full charge. Especially if we figure there is a little extra hidden headroom to start with. I know special things happen near the end of charge, but the charge controller should certainly know when it's in that region and respond accordingly.

Can anyone figure out what Nissan is worried about here?
And there goes the first capacity bar! At 24,000 mi on 9/9/2013.
Second bar at 30,500 mi on 2/7/2015.

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DaveEV
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Re: Charging from 80% to 100% -- What's the issue?

Thu Aug 04, 2011 3:25 pm

They're worried about people never taking it down below 80% and spending most of it's life at 80% charge or higher. Lithium batteries don't like to be stored when full.

ve2maa
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Re: Charging from 80% to 100% -- What's the issue?

Mon Jan 30, 2012 10:46 am

Is it really the only issue ???

If so, since I usually drive 40 miles a day, I shouldn't care about 80% or 100% !
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Nubo
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Re: Charging from 80% to 100% -- What's the issue?

Mon Jan 30, 2012 11:50 am

I'd love to see a definitive white paper on these kind of issues from Nissan's research. But I imagine that would open a can of worms both from a competitive standpoint as well as liability and complaints from overly-concerned owners. Similar as when Mazda decided to put a fake "oil pressure gauge" in my last car which was really only a glorified "idiot light". Seems they were tired of answering questions and concerns about normal pressure variability between hot and cold engines, etc...

My opinion is treat the battery as gently as you can but don't sacrifice utility or even convenience unnecessarily.
I noticed you're still working with polymers.

TangoKilo
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Re: Charging from 80% to 100% -- What's the issue?

Mon Jan 30, 2012 12:13 pm

I've got over 15,000 miles (58 miles per day avg.) and I've charged to 100% all the time. The dealer said my battery was in perfect condition at the 15k checkup the other day... 8-)

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LTLFTcomposite
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Re: Charging from 80% to 100% -- What's the issue?

Mon Jan 30, 2012 12:19 pm

TangoKilo wrote:I've got over 15,000 miles (58 miles per day avg.) and I've charged to 100% all the time. The dealer said my battery was in perfect condition at the 15k checkup the other day... 8-)
Do you have it timed so charging finishes shortly before you leave?

Although wasn't the question specifically about charging to 80%, and then later topping off to 100%? Although come to think of it, you can't charge to 100 without first charging to 80? Unless there is some concern about "pausing" the process at 80. I have done this a few times when I first thought I'd only need 80 then later decided I needed more range before I ever left and topped off to 100.
LTL
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GaslessInSeattle
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Re: Charging from 80% to 100% -- What's the issue?

Mon Jan 30, 2012 12:22 pm

My understanding of the recommendation was that it's fine to charge from 80% to 100% but that you should take it down to 80% or lower before charging up all the way, at least routinely. Then the winter came along and the car is getting prewarmed daily, definitely charging over 80% after previously charged to 80%. It's not unusual for me to prewarm all the way to 100%. For me, the question is how bad is it to prewarm after 100% charging. everyone routinely charging to 100% then prewarming appears to be allowed to "overcharge" the battery. seeing that most folks in the EV project are charging to 100% daily and prewarming, it seems if this were a problem, it could become a big problem. My conclusion is that Nissan has provided us with some general rules of thumb but for the most part have engineered out any ways to truly abuse the battery. I'm not worrying much about it. I charge to 80% and prewarm/top off as much as I need and figure the battery spends little time hanging out at 100% or however much over "100%" we are allowed to charge using prewarming if already at 100%.

from what I've read, the real issue with true 100% charging li-ion batteries is that leaving the battery at a high state of charge for long periods can lead to cladding of the anode/cathode and reduce capacity over time and it's within the upper 20% of the true 100% of the batteries capacity where more of the energy is lost to heat, and the heat is also degrading to the battery. there has been a lot of discussion about whether we are truly able to get at the true 100% of the battery or not, I tend to think we don't or at least we tend not to leave the car at a high enough charge long enough for it to really be a big issue. If the studies of li-ion batteries and cycle life apply to the Leaf's particular battery chemistry, it does seem to be worthwhile to reduce the time the battery spends at very high or very low charge states. Fortunately, the battery management system of the car makes it easy minimize impact based on the users preferences and needs. I have adopted the assumption expressed in other threads that time is ultimately going to rob the battery of capacity regardless of how it's charged. Ultimately though, I figure I'm way more likely to replace the battery before significant degradation occurs because a cheaper, higher capacity version will likely come out soon enough. How I charge this one will probably be moot.
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Nubo
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Re: Charging from 80% to 100% -- What's the issue?

Mon Jan 30, 2012 12:33 pm

My understanding is that another reason to go for 80% (if it suits your needs), is that the last 20% of charge is less efficient. Does anyone have a ballpark estimate to quantify that effect?
I noticed you're still working with polymers.

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ebill3
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Re: Charging from 80% to 100% -- What's the issue?

Mon Jan 30, 2012 12:34 pm

Well, I belive we have a little built in headroom.

To the best of my knowledge, 4.2 volts per cell is considered maximm full charge for Li Ion.
From my observations and those of others, a LEAF 100% charge yields almost exactly 4.1 volts per cell.

Bill
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KJD
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Re: Charging from 80% to 100% -- What's the issue?

Mon Jan 30, 2012 12:52 pm

TangoKilo wrote:I've got over 15,000 miles (58 miles per day avg.) and I've charged to 100% all the time. The dealer said my battery was in perfect condition at the 15k checkup the other day... 8-)
There is nothing wrong with charging to 100% and driving away, I do that a lot. By the time you get 10 or 15 miles down the road it will be down a couple of bars anyhow.

The only thing I would avoid is charging the car to 100% and then going on vacation for a month, now that would not be a good thing to do.

KJD
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