Does Running Battery Very Low Affect Capacity Over Time?

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Stoaty said:
Now, how about asking them why the first capacity bar is lost at 85%, rather than being evenly divided over the whole range? :twisted: I'm sure they would be very forthcoming on that as well. :D
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That would be to get you through the initial factory warranty period without complaining ;)
 
smkettner said:
Stoaty said:
Now, how about asking them why the first capacity bar is lost at 85%, rather than being evenly divided over the whole range? :twisted: I'm sure they would be very forthcoming on that as well. :D
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That would be to get you through the initial factory warranty period without complaining ;)
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Yes, that and it would allow Nissan to resell lease returns after 3 years without too much trouble.
 
With an 80% charge you really dont need much balancing, unless you have a poor thermal design or some bad modules.. but when you charge to 100% then you need to be balanced.. so perhaps thats when it happens, because its needed. Its automatic so we really dont need to talk about it.. no matter what we hash out its going to do its own thing anyways :)
 
TonyWilliams said:
DaveinOlyWA said:
ooooh, so we now believe that cell balancing happens ALL the time?? well, who has been saying that for OVER a year now?
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I don't think they said that, or really said anything. It's automatic. That's all you need to know.

The proletariat must return to the salt mines now.
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oh ya! use big words if you want! doesnt scare me! and besides!!...i have today off
 
Stoaty said:
GregH said:
Wasn't there some Recent post regarding Tesla's long term storage strategy where the battery was kept at a very low SOC? Down at 1 bar remaining the cells are still at a relatively happy 3.6v which should still be fine for most types of driving. When you get really low (no miles/bars left) that's when things get hairy.. By the time the turtle comes on the cells have sunk to nearly 3.0v at which point drawing high current is probably not wise. Just resting at 3.2 or 3.3v I don't know though... Maybe it's not so bad(?). Even though the car for some reason doesn't enforce this, I would drive really mellow (ie just a few bubbles of power) if there are no more bars showing.

On the high side from what I understand stress on the battery is a function of high voltage and/or high temperature AND time. Ie reaching 4.1v (100%) isn't so bad as long as doesn't sit like that for many hours. So for example if you more or less leave the house at 8am every weekday morning, you could set the timer with no start time and an 8am end time at 100% and the pack would only be at 4.1v for a short time... That wouldn't leave much time for cell balancing (if it were needed) although that's a different topic.. Personally I find the lack of regen at 100% rather annoying. I don't know exactly how to measure stress on the cells.. For example I couldnt say if resting at 4.1v for an hour is better or worse than resting at 4.05v (80%) for 10 hours.. Or resting at 100 degrees for an hour was better or worse than sitting at 90 degrees for 10 hours... Or resting at a very low voltage(?)
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Greg, do you have a list of the voltage at each number of bars showing? I would be interested in seeing a graph of this.
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I've been meaning to write this stuff down and do some discharge experiments at the low end but haven't as of yet. I'm away from my Leaf for another week but if memory serves, it was something like:
4.1v full
4.05v 80%/10 bars
3.75v 2 bars
And I think it was still over 3.6v when the last bar went away but it's been a while since I've been down that low. 3.6v btw is still perfectly healthy, I don't think there is any reason to avoid going down to 2 bars or even 1 bar. Personally I would avoid full throttle accelerations if I was deep into the last bar and the range number was flashing... But even here you're still at a healthy battery voltage. Things don't start falling off a cliff until the last bar vanishes at which point the voltage very quickly over 5 miles or so sinks from 3.6v (happy) to 3.0v (stressed). By the time the turtle comes on you're at 3.0-3.1v and internal resistance is so high that any moderate acceleration will force voltages to plummet. That's one thing that irks me about the Leaf.. In that last mile before turtle, you should not be allowed to do a full throttle acceleration.

My general rules of thumb are:
Charging to 100% is fine as long as the pack doesn't sit at over 80% for a long time (5+hrs)
Driving down to 1 bar is not a problem although probably wise to avoid full throttle acceleration when the range number is blinking.
If the last bar is gone and no range number, drive really mellow and plug in ASAP.
 
GregH said:
My general rules of thumb are:
Charging to 100% is fine as long as the pack doesn't sit at over 80% for a long time (5+hrs)
Driving down to 1 bar is not a problem although probably wise to avoid full throttle acceleration when the range number is blinking.
If the last bar is gone and no range number, drive really mellow and plug in ASAP.
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These sound like good rules of thumb, with some backing based on the voltage drop. Thanks!
 
GregH said:
My general rules of thumb are:
Charging to 100% is fine as long as the pack doesn't sit at over 80% for a long time (5+hrs)
Driving down to 1 bar is not a problem although probably wise to avoid full throttle acceleration when the range number is blinking.
If the last bar is gone and no range number, drive really mellow and plug in ASAP.
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What about in the 100% area... no problem with max acceleration, or continuous max power up a hill?
 
GregH said:
By the time the turtle comes on you're at 3.0-3.1v and internal resistance is so high that any moderate acceleration will force voltages to plummet. That's one thing that irks me about the Leaf.. In that last mile before turtle, you should not be allowed to do a full throttle acceleration.
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I have to wonder if the internal resistance of the pack is so low that it's able to push out 80kW even when nearly fully discharged without much voltage sag. After all, that's only about 3C discharge rate which is really nothing for a good quality lithium pack. Good cells can handle 5x that no problem.

TonyWilliams said:
What about in the 100% area... no problem with max acceleration, or continuous max power up a hill?
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Discharging quickly is not a problem from 100% and charging quickly is not a problem from 0%. The stress is on different parts of the cell when full and empty.

In general, the pack can discharge fastest when at 100% and can charge quickest when at 0%.
 
GregH said:
My general rules of thumb are:
Charging to 100% is fine as long as the pack doesn't sit at over 80% for a long time (5+hrs)
Driving down to 1 bar is not a problem although probably wise to avoid full throttle acceleration when the range number is blinking.
If the last bar is gone and no range number, drive really mellow and plug in ASAP.
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With those rules in mind, here's something to consider for those of us who normally charge (via timer) to 80%: If the battery is pretty low when we get home, rule 3 says we should plug-in ASAP. However, that requires a timer override which also has the side effect of charging all the way to 100%. So if you get home in the evening with a low battery, forcing an immediate charge means the pack will likely spend several hours at 100% before the car is driven again, unless you interrupt it mid-way and let the timer finish the charge later.

It also sounds like (even for us 80% chargers) it's probably better to set an end-time for charging rather a start-time. This bugs me as I hate passing any opportunity to charge (like closer to when I get home), since any late-night emergency (unplanned trip) or early morning power-failure could present a problem which could have been avoided.

I'm not sure I'd like to see the car's charge timer made any more complicated, but I can see an argument for a setting to "charge me a little right now if I'm really low, then stop, and finish it off in the morning".
 
I asked someone senior from Nissan:
"If you had a choice of only being able to charge between 0 and 50% or between 50% and 100% which would you pick."
Their response:
"It depends on how long you leave it at 100% before driving."

So, I gather leaving the car at 100% for long periods of time is worse than leaving it at "drained".

They offer a mode to stop charging at 80%, but they don't offer a mode to stop driving at 20%...

(Actually Tesla does have a mode where the car gets ready to quit at around 10% SOC, but you can change modes to switch to the battery "reserve" if you manage to get that low.)

Worst case is probably having a 100% full pack get hot and stay that way for a long time.
I hear the example of "in Phoenix"... Sustained desert heat + 100% SOC is not good for cell life.
 
My thought is that the worst thing you can do is charge a warm battery to 100% and then let it cool down. We know that a warm battery will hold more energy than a cold battery. If a fully charged battery cools down, does it end up overcharged? I don't know, but it seems like the extra energy must be somewhere.

Based on this, I am perfectly happy to charge to 100% between midnight and 8AM if I'm planning to drive that day.
 

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