agzand
Posts: 98
Joined: Tue Dec 22, 2020 3:00 pm

Re: Charging to 80% capacity

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
Posts: 922
Joined: Mon Sep 09, 2019 5:33 pm

Re: Charging to 80% capacity

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
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Star63
Posts: 41
Joined: Mon Sep 10, 2018 12:05 pm
Location: Finland

Re: Charging to 80% capacity

eNate wrote: Sun May 15, 2022 1:06 pm 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 :)
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eNate
Posts: 922
Joined: Mon Sep 09, 2019 5:33 pm

Re: Charging to 80% capacity

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.
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3pete
Posts: 206
Joined: Tue Mar 19, 2019 9:03 pm

Re: Charging to 80% capacity

agzand wrote: Tue May 17, 2022 8:51 pm 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
Posts: 206
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Re: Charging to 80% capacity

JohnWasser wrote: Sun Jun 05, 2022 8:20 am 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: :)
Star63 wrote: 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
Posts: 56
Joined: Sun Aug 29, 2021 4:53 am

Re: Charging to 80% capacity

eNate wrote: Sat May 28, 2022 7:46 am 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
Posts: 401
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Location: Hampshire UK

Re: Charging to 80% capacity

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?

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agzand
Posts: 98
Joined: Tue Dec 22, 2020 3:00 pm

Re: Charging to 80% capacity

Gonville wrote: Wed Jun 22, 2022 6:46 am
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
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Re: Charging to 80% capacity

Gonville wrote: Wed Jun 22, 2022 6:46 amAll 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.
Gonville wrote: Wed Jun 22, 2022 6:46 amAnyway 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.
Gonville wrote: Wed Jun 22, 2022 6:46 amSo? 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.
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