Charging 80 or 100%

[Maurice]

In the newer BMW’s like the I4 they recommend to charge to a max off 80% the keep the battery healthy.

Because of the BMS in the I3 some say to always charge the I3 to 100% because it needs 100% for battery calibration.

What is true?

 

[EvanstonI3]

The info that applies to the BMW i3. If it was otherwise they would have provided an option to set the charge to other than 100%.
100% on this car is not 100% because there is a buffer at the top and bottom ends, so the car ends up charging to 80-85% anyways but shows as "100%".

 

[eNate]

Most other EVs give their batteries top-end buffers, too. The biggest difference is that newer BMS systems have benefited from advancement of the technology, and can manage banks of cells with high precision.

My i3's 120Ah battery is 42.2 kWh total, 37.9 kWh usable, so just a bit more than a 10% buffer. But about half (I think actually 6%) is bottom buffer, so 100% indicated is 95% actual, and 0% indicated is about 5% actual. That's nowhere near 80%.

Compare that to my ID.4, which has double the battery but 6% buffer to play with -- so actually a larger buffer than the i3 if we're just looking at kWh excess capacity. There are a couple variants of the BMW i4, but the high one has a 4% buffer (83.9 kWh / 80.7 useable).

As I see it BMW committed to 100% with this car on account of the KISS principle: Keep it Simple... so as not to bother new BEV owners with the pesky complication of battery management. Once they chose that direction, they couldn't back out -- not without the expense of vehicle software updates, owner manual addendums, and facing the possibility claims to replace out-of-warranty deficient batteries (of which there have been a few). They didn't just do an about face on the i4 by allowing a user-selectable SOC cut-off, but they also allow the max rate of L2 charge to be stepped down from 48 to 32 or 20 or 16 amps, presumably in recognition of "less is more" which is especially true in warm summer months.

But BMW says charge tghe i3 to 100% and they don't make it easy to stop at 80. So I'm kind of in-between: do what you gotta do. I like to follow the industry norms and play it safe and stick with 80 indicated, which is actually easy for me to do. I just can't bring myself to letting my i3 sit around at 95% the majority of the time when the battery industry is pretty clear that cells are "happiest" living life in the middle.

BTW 100% (charging up from near 0%) helps with SOC calibration and estimating SOC correctly, but cell balancing occurs at rest at in-between SOCs, and a out-of-calibration SOC isn't going to impact how far the car can drive on a charge, only what it estimates it can drive on a charge.

 

[robthebold]

Battery management is religion. Pick the one that suits you and tell everyone else their batteries are -- metaphorically or literally -- going to hell.

 

[alohart]

The mi3 app reports that at an indicated 100% charge level, the actual charge level of our 2019 BEV is 96.1% which is much higher than 80%. Like eNate, I don't want to leave our battery pack at a high charge level any longer than necessary. Periodically, when I know that I will be driving soon, I charge to 100% to help the BMS calibrate its charge level calculation. For the same reason, I also discharge to 0% occasionally. I usually record what mi3 reports both at 0% and 100% to check how well cell charge level balancing is working (it seems to work very well) and to determine whether any cells are weak (none so far).

However, if managing the charge level is more than you would like to do, your battery pack will probably be fine always charging to 100%. Without a large sample, it's difficult to know whether this makes any difference over the long run.

 

[Chrism88]

100% is fine for a 2017 onward. I am at 102k on the 2017 and it’s hardly degraded at all. Newer cars use NCM 811 which swells more when top charging. The i3 uses NCM333 and I think 532 or 622, I can’t remember, which don’t suffer as much from top charging. It’s still not great to top charge but not as bad as modern cars.

 

[louisgrenier]

May be we should start to use better terms

Like 100% indicated

and then talk about what means a 100% indicated compare to the real limits of the battery cells

For my experience , a 2014 i3, always topped and kept at 100% indicated, I have lost 12 % since new of autonomy on 138 thousands kilometers Which I think is perfectly acceptable

The 12 volts battery still working. I can’t believe it !

Now I am looking at a AWD Volkswagen bus. And reading the manual, I see that they prefer you to charge at 80% indicated. Which is easy since they have a menu to stop the charging session to that level.

For whatever a 100% indicated in a i3 and a 80% indicated in a volks really means behind the software to the real capacities of the cells

 

[louisgrenier]

louis

 

[tongsli]

I charge to 100% and avoid DC fast charging if I can help it. I believe DC fast charging hurts the battery more than charging at level 2 to 100%. During the winter months I will charge with 120v overnight during the coldest temperatures.

 

[Bayrak]

I charge to 100% and avoid DC fast charging if I can help it. I believe DC fast charging hurts the battery more than charging at level 2 to 100%. During the winter months I will charge with 120v overnight during the coldest temperatures.

I do the same, set to 100% but 230v at home in UK never used DC charging.

 

[Darlouis]

I use a smart charger and charge to 100% rarely. I did today, in preparation for a 100 mile round trip but the car hit 100% about 20mins before departure.
Usually I'll charge to a 85 or 90% when running short trips locally , again, hitting that just before departure and not charge again until under 40% which for me at the moment this means a few weeks between charges as I don't use the car each day.
When I've checked using Electrified the cells are always well balanced.

 

[Ollie]

This is all internet hogwash. If the companies wanted "X". Then you would write the program to "X". This sounds like the olde wives tale about never putting a battery on concrete it will steal it's charge" Poppycock. What ****** marketing to sell you a product and then it be said that you can only use it at 80%. Also, if this was the case. They why isn't the solar industry parroting the same standard. My solar batteries are of the same material make-up. Now, all that being said. I 100% agree that the slower or lower input charge is always better than fast charging. But hey, that's what makes all of this fun and worth living IMO.

 

[ksnax]

KISS: i3s owners don't need to worry about this because BMW already did. End of story.

 

[duanew]

There are many naive statements above. Thinking that keeping lithium based batteries at high charge levels is good for them goes against chemistry and experience. Many times engineers have to make concessions to increase the ease of use of devices. I do not agree that BMW engineers only allow 100% charge because it is best. I advise that you try to not keep the batteries charged to high levels like every other EV suggests.

 

[alohart]

There are many naive statements above. Thinking that keeping lithium based batteries at high charge levels is good for them goes against chemistry and experience. Many times engineers have to make concessions to increase the ease of use of devices. I do not agree that BMW engineers only allow 100% charge because it is best. I advise that you try to not keep the batteries charged to high levels like every other EV suggests.

BMW engineers must have changed their minds, maybe due to many 60 Ah battery pack warranty replacements due to excessive usable capacity loss. For BMW's new EV's, they now recommend charging routinely to a displayed 80% unless more range might be required soon which should have been the i3 recommendation. However, that would have resulted in less range for an already low-range EV which would have probably hurt sales.

There's nothing magic about the i3 battery cells that would make them resistant to degradation when left for long periods of time at an indicated 100% charge level an actual charge level of ~95%, too high to minimize the cell degradation rate.

 

[Skye2002]

This is all internet hogwash. If the companies wanted "X". Then you would write the program to "X". This sounds like the olde wives tale about never putting a battery on concrete it will steal it's charge" Poppycock. What ****** marketing to sell you a product and then it be said that you can only use it at 80%. Also, if this was the case. They why isn't the solar industry parroting the same standard. My solar batteries are of the same material make-up. Now, all that being said. I 100% agree that the slower or lower input charge is always better than fast charging. But hey, that's what makes all of this fun and worth living IMO.

Well said...

 

[Gonville]

There are many naive statements above. Thinking that keeping lithium based batteries at high charge levels is good for them goes against chemistry and experience. Many times engineers have to make concessions to increase the ease of use of devices. I do not agree that BMW engineers only allow 100% charge because it is best. I advise that you try to not keep the batteries charged to high levels like every other EV suggests.

This ignores the fact that there is a top end ‘reserve’ not available which prevents charging above 85% actual? So unless one qualifies the remarks about ‘100%’ that advice in itself is worthless. The manual used to state leave it plugged in and there was no system iDrive mechanism to ‘stop’ at say 80% as there now is in the newer i models.

 

[Gonville]

BMW engineers must have changed their minds, maybe due to many 60 Ah battery pack warranty replacements due to excessive usable capacity loss. For BMW's new EV's, they now recommend charging routinely to a displayed 80% unless more range might be required soon which should have been the i3 recommendation. However, that would have resulted in less range for an already low-range EV which would have probably hurt sales.

There's nothing magic about the i3 battery cells that would make them resistant to degradation when left for long periods of time at an indicated 100% charge level an actual charge level of ~95%, too high to minimize the cell degradation rate.

Calendar degradation occurs irrespective of charge level. Thinking that a low level of charge which save on degradation is naive at best and misleading at worst. Calendar degradation is what it says. 1-2% per annum irrespective of charge level.

Also BMW engineered a refrigerating cooling system not present in the newer models and heat due to charging is indeed a factor.

 

[Gonville]

There are many naive statements above. Thinking that keeping lithium based batteries at high charge levels is good for them goes against chemistry and experience. Many times engineers have to make concessions to increase the ease of use of devices. I do not agree that BMW engineers only allow 100% charge because it is best. I advise that you try to not keep the batteries charged to high levels like every other EV suggests.

Cell balancing also is passive top end. That only happens on completion of charging when the level is above 85%. Indicated. If you only charge to 80% indicated the cells will become unbalanced and a reduction in charge capacity and therefore range will occur.

 

[alohart]

This ignores the fact that there is a top end ‘reserve’ not available which prevents charging above 85% actual?

That can't be correct! A 60 Ah battery pack has a 21.6 kWh gross capacity and 18.8 kWh usable capacity which is 87% of the gross capacity. That means that only 13% of the gross capacity is divided between low and high charge level buffers, so your 15% high charge level buffer size is impossible, especially because ~10% of the gross capacity is reserved for the low charge level buffer. This means that the size of the high charge level buffer is very small, less than 5%, which means that when fully charged, the actual charge level is >95%.

Attached is a screenshot of the mi3 app when connected to our 2019 BEV at a 100% charge level. The estimated battery pack state of health is 99%, so very little of its new usable capacity has been lost. In this case, the maximum actual charge level is 96.1% while the minimum actual charge level is 12.0%.

No one, including BMW these days, recommends leaving a lithium ion battery cell at a 96% charge level if one wants to minimize the cell degradation rate. However, if full range might be needed soon, charging to 100% is fine.