Charging to 80% capacity

[agzand]

Keep in mind that for BMW i4 97.1% of the battery is usable. For i3 it is about 90%. The i3 battery is also high cobalt, which helps with longevity. Gen 5 models use lower cobalt battery chemistry.

I think BMWs idea was that people will use departure time charging most of the time, so 10% buffer is adequate.

I have seen in other cars some drivers never charge to 100%, even for a road trip. I think that is absurd and pushing it too far. If you always charge to 80%, even on Level 2 for a road trip, then you are practically have 20% degradation in your new car. If you can live with that, then why are you worried about having the same 20% degradation in your car at 100k or 150k miles?

 

[eNate]

It's not a 10% buffer, it's 4-5% buffer, the other portion exists at the bottom end.

20% "degradation" by choice vs. actual degradation are two different things. When I've traveled in my i3, ABRP is really handy for indicating where I need 80% compared to legs I might need 95% or 100%, and there is a rather annoying time penalty that Is a factor in charging to 100 on a DCFC.

In any case, charging for traveling is entirely different from charging for day-to-day use – I don't see the comparison there

 

[Star63]

BMW tried to make the i3 "simple" and didn't even bother providing a means to limit charging.
Meanwhile, just about every EV before and after the i3's introduction suggests the 80% cut-off for daily use.

I use a 3 phase 11 kW AC charger that is connected to wifi. I can start and stop charging with my phone. I can also adjust the timer (start/stop) and the current settings remotely.
The most valuable feature to me is the capability to determine the amount or "dosage" of charge in kWh. You very quickly learn how many kWh you need to charge up to 80% or so. Quite satisfied with this

 

[eNate]

I ought to look if there's a portable L1 EVSE with a similar feature.

I primarily charge on 120 volts at work and reliablly take on 30% over 8 hours, so generally I only plug in if I'm near 50%.

My home EVSE is a "dumb' Clipper Creek which is too reliable to get rid of. The ID.4 my wife drives manages the 80% cut-off, so no need for the bells and whistles of a smart box.

 

[3pete]

You set departure times (up to three, for different days of the week). Make sure departure times are selected. Then you select "charge in time slot", instead of "charge immediately".

I use one departure time for weekdays (9 am), and one for weekends (11 am). These two are always active. The third departure time is set for early morning (6 am tomorrow) and usually deactivated. I activate it when I need to go out early to a job site. On weekdays usually I leave before 9 am, so the car is around 90% when I leave.

You can also set it on myBMW app. Again departure time works only if you charge in time slot.

Thanks-- I did try that out the other day and saw the charge graph on my juicebox that the car charged the way you described! I had assumed "charge in timeslot" meant it would start charging as soon as the timeslot opened which is also how I would have programmed it. Or, maybe charge up to 80% ASAP, then wait until the last minute to fill up the rest of the way. Or, assume the car would charge during the whole window and lower the rate to reach 100% at the very end (assuming that lower current is better for the battery life).

I'm sure this would be a rare scenario but if I'm understanding correctly, BMW's choice on behavior means you could plug in at 7pm with a charge window from 10pm to 7am and if your power went out at 3am you'd be in a whole heap of trouble when you woke up the next day, even though the car had plenty of time to charge in the low-cost window to complete.

 

[3pete]

Side note: One of the newer Level 2 charging stations in my area has a button you can press to stop charging at 80%.

This is interesting because my understand of L2/ J1772 is that the state of charge for the car is not communicated to the EVSE like it is over CCS. So it would be impossible for the L2 station to know when your car hits 80%. However, it would also seem like a trivial bit of code to add an option that essentially says: as soon as the car starts lowering it's requested current, assume it's around 80% and shut off the charge.

One thing that would be a little bit tricky would be that lower L2 charge rates (16amp for instance) wouldn't actually correspond to 80% when current drops, and L1 probably gets throttled closer to 95% or higher. It'd be a more consistent threshold than Star63's approach, though not as reliable to end at the same charge state:

The most valuable feature to me is the capability to determine the amount or "dosage" of charge in kWh. You very quickly learn how many kWh you need to charge up to 80% or so. Quite satisfied with this

This actually would also be interesting to do in hotter climates to get an idea for how much juice the battery cooling uses. Chilly days you might charge up to 80% whereas the same calculation on a hot day might be closer to 75%.

 

[Skyking6976]

I always hesitate before replying to the 100% threads because BMW says to do it, and gives us no useful tools to stop the charge.

But I have point out that, as you say you don't drive much, about the worst thing for a battery is to store it at a full or depleted state of charge. I'm not making the distinction between 100% and 94% but talking 70%.

And to be clear, 199 miles on the GOM isn't an indication of a battery's health, it's representative of a car that's been driven conservatively and efficiently – so good job there! – but I wouldn't expect to see any ill effects on a '21 anyhow.

I get it, especially with a lease and no skin in the game. But for somebody planning to hang on to their i3 for the long term, observing what's essentially industry standard charging norms isn't a guarantee of anything, but is simply cheap insurance for a long and bountiful battery life.

Just saw this. Gotcha and thanks.

 

[Gonville]

I know this is an old topic and complicated by the arrival of new models.

I have updated to a 94Ah i3 and MiniSE which was traded in for an LCI Mini SE.

All our experience was that passive cell balancing was an essential part of the i3 charge strategy and occurred only above 85%. Ignoring usable buffers here. I managed to get a 60Ah 2014 down to 33m GOM by only part charging.

Anyway the latest i3, and iX3, manual has changed the advice to only charge to 80%. Manual dated FEB 22.

In addition they have changed it to say don’t leave plugged in anymore. For an idle period whereas before that was always to plug in to protect the 12v.

So? What’s changed? Cut and paste from newer models? Different chemistry? Idrive 8? What?

And big question. What happened to passive cell balancing?

 

[agzand]

Anyway the latest i3, and iX3, manual has changed the advice to only charge to 80%. Manual dated FEB 22.

I assume you mean latest i4? The i3 doesn't have a setting to limit to 80%.

 

[alohart]

All our experience was that passive cell balancing was an essential part of the i3 charge strategy and occurred only above 85%. Ignoring usable buffers here. I managed to get a 60Ah 2014 down to 33m GOM by only part charging.

I limited charging in our 2014 BEV for more than 7 years yet the mi3 app has always reported almost no charge level, voltage, or capacity differences between the weakest and strongest cells in each of these categories. Is there any reason why passive cell balancing couldn't occur below 85% absolute charge level? I can understand why cell balancing would be slower at lower charge levels because of lower cell voltages, but with the goal of passive cell balancing being to equalize cell voltages, it would seem that this could occur at any charge level.

Anyway the latest i3, and iX3, manual has changed the advice to only charge to 80%. Manual dated FEB 22.

In addition they have changed it to say don’t leave plugged in anymore. For an idle period whereas before that was always to plug in to protect the 12v.

I have generally followed this advice even though the i3 Owner's Manual offered different advice. The new advice agrees with what Li-ion battery cell experts generally suggest for minimizing cell degradation.

So? What’s changed? Cut and paste from newer models? Different chemistry? Idrive 8? What?

Maybe the experience of many 60 Ah i3 owners whose battery packs have lost significant usable capacity has resulted in BMW changing its recommendations to agree with experts.

 

[eNate]

I recall reading fairly convincing proof (from the archives, here in this forum) cell balancing occurs at lower states of charge.

But because balancing relies on voltage, it's most effective at high SOCs where there's a meaningful difference between hundredths of a point, where for mid SOCs it's pretty flat.

 

[alex29a]

I constantly keep my ( now 37000 miles ) 94Ah ( Rex ) Charged up to 100% using the slow home 10A granny charger
as soon as I have used 30-40 miles and the % falls to around 68-70% , it's on charge for around 4-5 hours

I am happy with that, having peace of mind full range.
So far the battery behaviour has been consistant on all the usage/charge readings.
showing no sign of degradation.

I have also left it sitting 100% fully charged for 15 Days when was on holiday.
No effect on anything

Perhaps ?? is it becase a slow charge has less harmful effect on the battery
than fast charge ..? if anyone can comment of that

 

[alohart]

So far the battery behaviour has been consistant on all the usage/charge readings. showing no sign of degradation.

Noticing mild degradation can be difficult. The free mi3 app (iOS) or electrified app (Android) reports the battery pack state of health which is probably a better indication of degradation than trying to associate usable battery capacity with range that fluctuates with temperature, driving conditions, tire inflation pressure, and several other factors.

I have also left it sitting 100% fully charged for 15 Days when was on holiday. No effect on anything

Maybe, maybe not. 15 days isn't terribly long, but the effects could take a while to be noticeable. BMW warns about leaving the charge level too low, but doing so would likely not be immediately noticeable. Degradation occurs slowly over time, so for those who want to minimize degradation, it's best to avoid doing things that experts advise against.

Perhaps ?? is it becase a slow charge has less harmful effect on the battery
than fast charge ..? if anyone can comment of that

1 C is the charging power that would charge a battery pack from 0% to 100% in 1 hour. 240 VAC Level 2 charging at 30 A (7.2 kW) isn't fast (only 0.22 C for your 33 kWh battery pack). It's probably no worse than 120 VAC Level 1 charging at 10 A (1.2 kW or 0.04 C). DC fast charging (50 kW or 1.5 C) might be more harmful than AC Levels 1 or 2 charging, but those who have looked for evidence of this haven't found much. Other EV's charge at C rates greater than the i3 yet don't suffer much battery cell degradation. If one charged only using DC fast chargers, degradation might be greater over several years than had one charged at AC Levels 1 or 2.

 

[Gonville]

Anyway the latest i3, and iX3, manual has changed the advice to only charge to 80%. Manual dated FEB 22.

I assume you mean latest i4? The i3 doesn't have a setting to limit to 80%.

No I don’t mean that. The latest i3 manual and the latest Mini SE manuals both say don’t leave it plugged in for long periods and don’t charge past 80%. There are no tools true.

Our view is that it means on DC due to charge rate decline rather than AC but that isn’t clear.

 

[Gonville]

So? What’s changed? Cut and paste from newer models? Different chemistry? Idrive 8? What?

Maybe the experience of many 60 Ah i3 owners whose battery packs have lost significant usable capacity has resulted in BMW changing its recommendations to agree with experts.
[/quote]

I don’t agree. The battery experts at battery university are nearly always taking about single cell systems in a laboratory with no thermal management and 1C charge and discharge rates. We are talking about a multi cell with active thermal management system and specific charge buffer allocations. Engineer versus Chemistry. Expert engineers versus expert chemists/physicists.

Nothing we can do about the 1-2% calendar degradation.

As an aside in the U.K. our group with 6,000 members has had only 1 60Ah vehicle have a failed cell replaced under warranty. No 70% battery capacity warranty claims. I think the USA has higher overall temperatures environment and that is an issue I guess.

 

[johnnyz383]

I installed electrify and found out some very interesting things about my pack. I have 6 years experience building lithium packs and know a thing about these cells. My 2015 i3 with 72000 kms had a KAPPA reading of anywhere from 16.2 to 14.9. I also noticed after a dealer update that the pack would seemingly lose percentage without the car doing anything. After initializing the electrified app I found that 1) The battery is 100% solid. 2) The cell balance was within a tenth of a volt. 3) At 100% state of charge (What the BMS is reporting) the pack is at 4.1 volts per cell, and at 20% the pack is only at 3.76 volts!. 4) There is a .5 of amp residual draw even with the car off. 5) I can now ascertain that the pack has MORE capacity than the BMS is reporting, even when you factor in the unusable upper and lower capacity. Time to see if the BMS can be reset, as it appears the BMS is taking into account time and artificially deflating the degredation of the pack. Simply absurd.

 

[alohart]

Older versions of BMW’s ISTA+ software support initializing the BMS. It must be installed on a Windows laptop and connected to the OBD port with an Ethernet cable that can be purchased online (WiFi and Bluetooth not supported). I don’t have any experience with ISTA+, but several mostly European i3 owners have reported some success at increasing the battery pack’s usable capacity, at least for a few months until the BMS is initialized again. I chose not to try this until my battery pack warranty expired.

 

[Cyberj]

This is way overthinking it. BMW i3 battery life has had very good reviews so far. YouTuber Engineering Explained has an excellent video about charging and battery life. Drive as you like. Charge when you want. It will be fine.

 

[alohart]

This is way overthinking it. BMW i3 battery life has had very good reviews so far. YouTuber Engineering Explained has an excellent video about charging and battery life. Drive as you like. Charge when you want. It will be fine.

i3's have had battery cells with 3 different battery chemistries. Some but not all 60 Ah cells seem to degrade more rapidly than expected resulting in battery packs being replaced at no cost under BMW's battery pack capacity loss warranty. I know of 4 such replacements locally where ambient temperatures are never extreme (Hawaiʻi). Their owners always charged fully, some leaving an EVSE plugged in whenever their i3's were parked at home. I limited my routine charge of our 2014 i3 to ~80% unless I might need more range soon thereafter. Our battery pack didn't degrade enough to be replaced under warranty but more than I would have liked considering the low range even when new.

I replaced our 2014 BEV with a 2019 BEV because its range had decreased so much that we could no longer drive round-trip to some destinations that we enjoyed visiting. Fortunately, DC fast chargers were available, but they were increasingly busy and sometimes not working making these trips more stressful and lengthy than we'd prefer. Our former 2019 BEV and current 2021 BEV can easily travel round-trip anywhere we want to go without having to charge en route.

Using the mi3 app, I can see that our 120 Ah battery cells aren't degrading nearly as rapidly as our 60 Ah battery cells even accounting for only half as many charge-discharge cycles due to their double capacity. I still don't routinely charge to 100%. It seems that 94 Ah battery cells are more stable than some 60 Ah cells as well.

 

[ksnax]

While battery chemistry itself is to some degree responsible, power density tends to be the more significant factor. I.e., because the 60Ah cars must use 2x the capacity of the cells in the car vs a 120Ah one, they are essentially getting cycled twice as often - which is a major driver of decay. So if a 60Ah pack may go as far as 100k miles, it would take the 120Ah pack 200k miles under the same use and charging circumstances. So there is a perception among many that newer cells are more tolerant of fully cycling and that older cells benefit from more shallow cycles, it's all ultimately the same with respect to the quantity of Watts put in and pulled out.

I don't have the reference handy, but a Youtuber covered this issue well specifically for the i3, using data collected from owners and dealers accounting for miles driven, age, and pack size. Age barely figured into it (supporting the lower significance of chemistry).