Charge to 80%?

[EHM Bellevue]

The standard advice for non-LFP batteries is to charge routinely to 80%. The very thoughtful and thorough engineers who designed the i3 have made this difficult. I can only conclude that their view is that customers should simply charge to 100% routinely.

We have a 2021 i3 (i.e., the big battery) and absolutely love the car. It is just so shockingly well engineered and thought-through that it takes your breath away. On something as important as the battery pack it's impossible for me to over to believe that the engineer is overlooked this issue.

I recognize that there are settings, which we use, which allow the charging to start automatically from your home charger during off peak hours, in order to reduce the load on the grid as a whole during period of peak useage from 4:30PM to about 8:30PM. And yes, I know, and i3 doesn't and cannot put much strain on the grid, but it's just wholesome citizenship to use this setting.

We’re perhaps paying more attention to this issue than it warrants. But since there is no “charge to just 80%" feature on the charging menu, I select the recharging to start at an hour and amperage whereby the car will be about 80% charged when I finish breakfast. I then go downstairs to the garage and manually stop the charging (at 79 to 82%). But given how well-engineered everything else on the car is, I suspect that this is silly and I should just let it charge until it shuts itself off at 100%/160 miles of range.

Any thoughts, data or input on the issue?

 

[mojo]

Being an i3-specific forum, it has been asked and answered (with thoughts and opinions) many times here before.

If you put "Charge to 80" in the search box you will find a lot of previous threads on the subject.

 

[JohnnyCakes]

The i3 has an excellent battery management system. Feel free to charge to 100%.

That said, at a public charger, after 80% charge the rate slows for all vehicles, not just the i3. If people are waiting for the charger, it's rude to charge over 80% unless your journey absolutely requires it.

 

[eNate]

I just time it. I charge at work and have an amperage-adjustable / time-delayable L1/L2 EVSE that can give as little as 10% over an 8 hour day, up to 30%, or even 60% if I Level-Two it. And the timer can delay the start of charging for 2, 4, 6, or 8 hours. So I can pretty easily target 80%.

And if I go over (or under) I don't sweat it. But usually I can be within a few percent.

Obviously at home that would be a little different because I'm out the door at different times, but it's still a workable solution.

BMW will never give us an 80% option on this car, but it sure would be nice to add a "Stop Charge" button to the app.

 

[alohart]

The i3 has an excellent battery management system. Feel free to charge to 100%.

That said, at a public charger, after 80% charge the rate slows for all vehicles, not just the i3. If people are waiting for the charger, it's rude to charge over 80% unless your journey absolutely requires it.

The 120 Ah battery pack reaches its 50 kW DC fast charging power peak at a charge level of 86% dropping to 35 kW by a charge level of 90%. So it wouldn't be rude to charge to 86% or even 90%.

 

[EHM Bellevue]

The i3 has an excellent battery management system. Feel free to charge to 100%.

That said, at a public charger, after 80% charge the rate slows for all vehicles, not just the i3. If people are waiting for the charger, it's rude to charge over 80% unless your journey absolutely requires it.

Thank you!!!

 

[EHM Bellevue]

The 120 Ah battery pack reaches its 50 kW DC fast charging power peak at a charge level of 86% dropping to 35 kW by a charge level of 90%. So it wouldn't be rude to charge to 86% or even 90%.

View attachment 1293

Wow. Great data. Thanks so much. Just getting in the swing and appreciate help from fellow i3 owners.

 

[EHM Bellevue]

The i3 has an excellent battery management system. Feel free to charge to 100%.

That said, at a public charger, after 80% charge the rate slows for all vehicles, not just the i3. If people are waiting for the charger, it's rude to charge over 80% unless your journey absolutely requires it.

Great feedback. And yes, I will be a "good citizen" especially on high-speed 350kW chargers like the EA unit I used this AM.

 

[EHM Bellevue]

Being an i3-specific forum, it has been asked and answered (with thoughts and opinions) many times here before.

If you put "Charge to 80" in the search box you will find a lot of previous threads on the subject.

Thank you! Will search.

 

[sailnavy]

It’s almost like the engineers on the i3 took a different approach. You’re fine charging to 100%.

 

[EHM Bellevue]

It’s almost like the engineers on the i3 took a different approach. You’re fine charging to 100%.

Thank you for your feedback. Yes, on so many things the "engineers took a different approach", which is part of the fantastic attraction of the car ...

 

[JohnnyCakes]

The 120 Ah battery pack reaches its 50 kW DC fast charging power peak at a charge level of 86% dropping to 35 kW by a charge level of 90%. So it wouldn't be rude to charge to 86% or even 90%.

View attachment 1293

Interesting. I guess our i3's are special The rule of thumb is 80% (posted throughout the Internet) so I'm gonna print out your post and distribute it to all the waiting drivers giving me an evil eye over 80%!!

 

[eNate]

Interesting. I guess our i3's are special The rule of thumb is 80% (posted throughout the Internet) so I'm gonna print out your post and distribute it to all the waiting drivers giving me an evil eye over 80%!!

Yep the BMW engineers of 10-15 years ago had some magic allowing them to ignore battery charging norms and best practices that they forgot to pass down to today's BMW engineers.

Or was it that they didn't want to burden the prefers of their short range car with 80% cutoffs and battery management "rules" in favor of the KISS principle, and it would be disastrous reversing that decision because it would open them up to an expensive software update campaign and litigation by owners needing battery replacements out of warranty?

 

[CJP]

Hi.

I charge to 80% as recommended by the Australian university of battery charging, yes it does exist. Thus allowing the maximum number of charges per battery life. If you require the graph I can send.
I use my determined method of
80 - current % x 3.65 = time in minutes.
Allowing me to time, in the comfort of my chair and turn of my charger by phone interaction.

It is sad that BMW got the charging bad, but as you say everything else is marvelous.
Regards Chris

 

[EHM Bellevue]

Yep the BMW engineers of 10-15 years ago had some magic allowing them to ignore battery charging norms and best practices that they forgot to pass down to today's BMW engineers.

Or was it that they didn't want to burden the prefers of their short range car with 80% cutoffs and battery management "rules" in favor of the KISS principle, and it would be disastrous reversing that decision because it would open them up to an expensive software update campaign and litigation by owners needing battery replacements out of warranty?

I would rather think, given the amazing engineering of the rest of the car, that they just opted for a modest, and flat charging "curve" rather than succumbing to the siren song faster charging below 80%.

 

[EHM Bellevue]

Hi.

I charge to 80% as recommended by the Australian university of battery charging, yes it does exist. Thus allowing the maximum number of charges per battery life. If you require the graph I can send.
I use my determined method of
80 - current % x 3.65 = time in minutes.
Allowing me to time, in the comfort of my chair and turn of my charger by phone interaction.

It is sad that BMW got the charging bad, but as you say everything else is marvelous.
Regards Chris

Thank you for taking the time to contribute to the thread. I have the BMW portable L1 and a Tesla L2 charger with the NACS-to-CCS Lectron adaptor at home (my other car is a Tesla, and I like them both, but I have come to LOVE the i3). I also successfully charged, briefly, just to test at a L3 charger yesterday. I think you're right to note that the number of charge/discharge cycles is an important variable as well, perhaps more important, as other literature suggests that 2,500 cycles is about the max for most high-quality lithium batteries. They don't die at this level, just this is when they enter a period of substantially degraded performance.

Earlier in this and related threads, a member suggested that his driving requires one-a-week charging, and frankly our use case is similar. Especially since we have another car, I am tempted to just take this approach and start charging whenever we finish using the car on Sunday and let it charge from ~4PM to 9AM. We're retired, so we have this big "window" for letting it use the L1 charge rate to restore it to "full".

 

[eNate]

I would rather think, given the amazing engineering of the rest of the car, that they just opted for a modest, and flat charging "curve" rather than succumbing to the siren song faster charging below 80%.

There is no curve when L1 charging, and none that that I've notched in 40 amp L2. Not on the i3, not on my ID.4, and from what but and pieces I've read for other makes and models. From that standpoint, a state of charge is what it is, with no regard for how it got there.

Frankly, this conversation has been rehashed so many times, but the end result is the same: BMW instructs owners to charge to 100%, so everyone should feel assured in doing so. Yet despite the claims of superior engineering and fat buffers, no such evidence supports this, and there is no denying that (a) this car was designed in 2010-2012 and battery technology has steadily improved in that time, coupled with (b) practically every other EV, including new BMWs, sticks to the 80% suggestion, with methods provided for owners to manage their charge.

 

[alohart]

Interesting. I guess our i3's are special The rule of thumb is 80% (posted throughout the Internet) so I'm gonna print out your post and distribute it to all the waiting drivers giving me an evil eye over 80%!!

Those i3 owners with 60 Ah battery packs who DC fast charge beyond 80% should get the evil eye from those waiting to charge. At 80%, the DC fast charging power would be reduced to only 20 kW.

 

[alohart]

Yep the BMW engineers of 10-15 years ago had some magic allowing them to ignore battery charging norms and best practices that they forgot to pass down to today's BMW engineers.

Or was it that they didn't want to burden the prefers of their short range car with 80% cutoffs and battery management "rules" in favor of the KISS principle, and it would be disastrous reversing that decision because it would open them up to an expensive software update campaign and litigation by owners needing battery replacements out of warranty?

I'll vote for the latter. BMW has had to replace many 60 Ah battery packs under their capacity warranty. Had these owners had an 80% charge level limit choice, battery cell degradation might not have been so significant. Fortunately, 94 Ah and 120 Ah battery cells seem to be much more resistant to rapid degradation.

 

[alohart]

There is no curve when L1 charging, and none that that I've notched in 40 amp L2. Not on the i3, not on my ID.4, and from what but and pieces I've read for other makes and models. From that standpoint, a state of charge is what it is, with no regard for how it got there.

The maximum AC Level 1 charging current is only 10A unless one has a 2014 i3 occasional use cable or 3rd-party EVSE with a maximum charging current of 12A. While the i3's on-board charger does reduce the AC charging current as the charge level approaches 100%, it's not noticeable during the relatively slow AC Level 1 charging.

When charging on our 208V 20A AC Level 2 charging circuit with a JuiceBox EVSE that displays the current, I have watched the current decrease from its 16A maximum as the charge level approaches 100%. However, our charging power is relatively low (3.3 kW max), so I don't notice the slight reduction in charging speed.