On decreased capacity battery-Is charging 100% still bad?

[MrFish]

A question for those who have a better understanding of the Leaf battery chemistry and BMS.

My battery only has 11 capacity bars now. My understanding is that the BMS is limiting capacity due to a few weaker cells that are limiting charge to the entire pack. So my question is this: Since a few weaker cells are already limiting the amount of charge to the remaining cells, is there any benefit in limiting my charge to 80% anymore? Due to the decreased range, charging to 100% would help, but I don't want to degrade the pack any faster than I have to.

My logic is that even a 100% charge is only going to be 100% to the few weak cells, the rest of the "good" cells will never see a 100% charge because of the BMS.

I appreciate any thoughts on the subject.

Mike

 

[mwalsh]

Charge as you need to charge. It's not been proven adequately (IMHO) that charging to 80% is any more beneficial. I've been charging to 100% from day one, unless it a day I don't expect to need the car, and I don't think it's done me any injury beyond anticipated losses.

 

[DaveEV]

My logic is that even a 100% charge is only going to be 100% to the few weak cells, the rest of the "good" cells will never see a 100% charge because of the BMS.

The battery pack is top-balanced, so all cells see the same voltage when charged to 100%.

 

[MrFish]

My logic is that even a 100% charge is only going to be 100% to the few weak cells, the rest of the "good" cells will never see a 100% charge because of the BMS.

The battery pack is top-balanced, so all cells see the same voltage when charged to 100%.

the top-balanced voltage seen by all the cells will be limited to the weakest cells ability to accept a charge, correct? I'm still trying to get my mind around how the BMS works.

So if the weaker cell will only accept say 4.0 volts, then all the cells, even the healthy ones, will only see 4.0 volts. Thus, the healthy cell will never again charge to their potential of 4.2 volts due to the BMS limiting them to the voltage of the weaker cell. In my mind that would mean that even a 100% charge would in fact not be 100% to the healthy cells, only to the weaker cells.

Am I correct?

 

[Stanton]

Charge as you need to charge. It's not been proven adequately (IMHO) that charging to 80% is any more beneficial. I've been charging to 100% from day one, unless it a day I don't expect to need the car, and I don't think it's done me any injury beyond anticipated losses.

I don't see how you can say this given what we know degrades battery capacity/life, in no particular order:
1) heat
2) charge cycles (effectively miles)
3) time spent @100% SOC (and some would say the lower the better)

You may not live in a hot climate, but the OP might (his city isn't in his profile). So, I would say: charge to 80% (as a default) UNLESS you need the extra range that 100% provides, and drive it within a few hours of reaching a full charge. This is what's worked for me and I live in a hot climate.

 

[MrFish]

Charge as you need to charge. It's not been proven adequately (IMHO) that charging to 80% is any more beneficial. I've been charging to 100% from day one, unless it a day I don't expect to need the car, and I don't think it's done me any injury beyond anticipated losses.

I don't see how you can say this given what we know degrades battery capacity/life, in no particular order:
1) heat
2) charge cycles (effectively miles)
3) time spent @100% SOC (and some would say the lower the better)

You may not live in a hot climate, but the OP might (his city isn't in his profile). So, I would say: charge to 80% (as a default) UNLESS you need the extra range that 100% provides, and drive it within a few hours of reaching a full charge. This is what's worked for me and I live in a hot climate.

I get what your saying, but what I guess I'm asking is 100% still 100% when the BMS in actually limiting the healthy cells to less than 100%?

 

[leafwing]

Charge as you need to charge. It's not been proven adequately (IMHO) that charging to 80% is any more beneficial. I've been charging to 100% from day one, unless it a day I don't expect to need the car, and I don't think it's done me any injury beyond anticipated losses.

I don't see how you can say this given what we know degrades battery capacity/life, in no particular order:
1) heat
2) charge cycles (effectively miles)
3) time spent @100% SOC (and some would say the lower the better)

You may not live in a hot climate, but the OP might (his city isn't in his profile). So, I would say: charge to 80% (as a default) UNLESS you need the extra range that 100% provides, and drive it within a few hours of reaching a full charge. This is what's worked for me and I live in a hot climate.

I get what your saying, but what I guess I'm asking is 100% still 100% when the BMS in actually limiting the healthy cells to less than 100%?

Why don't you call Nissan? They might know something about this.

 

[Stanton]

I get what your saying, but what I guess I'm asking is 100% still 100% when the BMS in actually limiting the healthy cells to less than 100%?

Maybe someone can give a more technical answer, but my understanding is once you start losing bars, the BMS's definition of 100% changes (declines). Up to a point, I think it's still beneficial not to "top off" the battery pack, but I suspect once you start losing >2 bars (for example), it becomes irrelevant because you may need a 100% charge just to get a minimum useable capacity.

 

[mwalsh]

I don't see how you can say this given what we know degrades battery capacity/life, in no particular order:
1) heat
2) charge cycles (effectively miles)
3) time spent @100% SOC (and some would say the lower the better)

You may not live in a hot climate, but the OP might (his city isn't in his profile). So, I would say: charge to 80% (as a default) UNLESS you need the extra range that 100% provides, and drive it within a few hours of reaching a full charge. This is what's worked for me and I live in a hot climate.

Hey, if 80% isn't cutting it anymore, then the options are pretty darn limited. No?

 

[Herm]

I get what your saying, but what I guess I'm asking is 100% still 100% when the BMS in actually limiting the healthy cells to less than 100%?

Even the weak cells can be charged to 100%, which is 4.1V per cell.. but since all the cell pairs are wired in a string then the car simply stops when the weakest cells dies.. think of an old style xmas light string. Yes there is still range left in the other cells but if the BMS would allow you to use that then the weak cells would be destroyed, perhaps even catch fire. If you replaced the weak module then the next weakest module would determine the overall range.

You should not assume your range degradation is due a few weak modules..

 

[KJD]

My logic is that even a 100% charge is only going to be 100% to the few weak cells, the rest of the "good" cells will never see a 100% charge because of the BMS.
I appreciate any thoughts on the subject.
Mike

What city are you located in ?

How many days do you see the temps get over 100F ?

As a rule I charge to 80% daily and use the END ONLY timer. The timer is set to finish just before I leave for work in the morning. This strategy keeps the SOC as low as possible as long as possible. It also allows charging at the lowest temp of the night (morning).

If you really do need 100% charge then by all means use it, just make sure you drive the car as soon as it finishes charging. I never let the car sit in the heat of the day at 100% SOC.

 

[Kgbnsf]

We're 18 months into our lease and always charged at 100%. We occasionally 'top it off' before longer trips by re-plugging the car back in at the end of the charging cycle and getting another 30 minutes of charging which seems to allow us to get further on the first bar. We have quick charged it (440v) three times. We have not noticed any drop in range. I think we'll be fine for the next 18 months. We just brought it in for the service and the battery tested fine. From a factual standpoint, I am sure there has been some degradation; it just hasn't been bad enough for us to notice.

If I bought rather than leased, I would give the 80% charge cycles more consideration. I just need 3 years from it and 1/2 way there it's been great.

 

[Nubo]

... As a rule I charge to 80% daily and use the END ONLY timer. The timer is set to finish just before I leave for work in the morning. This strategy keeps the SOC as low as possible as long as possible. It also allows charging at the lowest temp of the night (morning).

If you really do need 100% charge then by all means use it, just make sure you drive the car as soon as it finishes charging. ...

Same here. 80% is more than enough for my weekday use and an end-timer fits my needs. On the weekends we'll typically need 100% for one or both days. The 80% end-timer does the bulk of the charge and there's enough time in the morning to top to 100% so that the time at 100 SOC is minimized.

AFAIK, charging is based on voltage, not kWH. The bad things that happen near the top of charge are driven by voltage. So I wouldn't expect that to change just because the capacity has reduced. If anything, I'd take it as a sign to be as careful as possible with the pack. But, the car is meant to be used so if you need 100%, charge to 100%. Being careful with the timing will help.