Derek2
Posts: 7
Joined: Wed Sep 22, 2021 12:48 am

Charging to 80% capacity

Should we i3 owners charge the car fully or to 80% to preserve the battery?
JohnKelly
Posts: 116
Joined: Sat Oct 07, 2017 7:02 am

Re: Charging to 80% capacity

No. The BMS takes care of that for you. There is an upper and lower battery buffer. Why add more buffer, and thus reduce range?
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eNate
Posts: 921
Joined: Mon Sep 09, 2019 5:33 pm

Re: Charging to 80% capacity

I would (I do).

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.

Owners often cite the i3's buffer, But other EVs have battery buffers as well, and frankly the i3's buffer doesn't add up to 20%. On top of that, a significant portion of the buffer (difference between usable and total capacity) is reserved for the bottom end -- the car can't discharge down to true 0%, either (as can't other EVs). That puts the top end buffer at around 95% of the pack's total capacity, depending on year and pack size.

And this is using 2013 battery technology! Consider the ID.4 which I also own has a very new, very precise battery management system still comes with an 80% suggestion from VW.

Likewise, even BMW with their new i4 and iX is providing an 80% suggestion, plus charge limiting, and even current limiting.

There are plenty of arguments that regularly charging the i3 (or any other EV) to 100% has not shown any substantial degradation, and for that, I don't have a good answer. Other data does. We've seen that the early i3s suffered accelerated battery degradation but that could be for any number of reasons -- battery technology, pack size, charging habits, who knows. Likewise, there is a lot of mixed data out there for other brands of EVs as well.

So to that I say this: if all manufacturers (of cars and batteries) recommend 80%, and it doesn't interfere with your day to day use of the car, why not? What secret sauce did BMW have for the i3 in 2013 that nobody else seems willing to reconstitute, including BMW? If, on the other hand, it's impractical or you don't care or you know you won't own the car in 5 or 8 years or you actually need 100% range for day to day use, then do it, BMW says it's OK.
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agzand
Posts: 98
Joined: Tue Dec 22, 2020 3:00 pm

Re: Charging to 80% capacity

BMW came up with departure time charging scheme for the i3, the hope is that you won't let the car sit at 100% charge for extended periods. If you charge to 100% using departure time, it is OK. The problems arise when you charge to 100% and the car sits for a few days, or weeks.
3pete
Posts: 206
Joined: Tue Mar 19, 2019 9:03 pm

Re: Charging to 80% capacity

agzand wrote: Mon May 16, 2022 10:13 am BMW came up with departure time charging scheme for the i3, the hope is that you won't let the car sit at 100% charge for extended periods. If you charge to 100% using departure time, it is OK. The problems arise when you charge to 100% and the car sits for a few days, or weeks.
Departure time charging scheme? When was this introduced and how do you get to it?

Are you saying it allows you to tell the car you're leaving at 7am tomorrow and it will charge to 80% immediately then wait to charge the rest of the way so it hits 100% at 7am?

I have only ever noticed the departure time to impact:
1) Battery conditioning overnight and pre-departure
2) Cabin pre-heating or cooling pre-departure
3) A notification that your car will not be charged to 100% if your departure time does not allow enough charging time.
3pete
Posts: 206
Joined: Tue Mar 19, 2019 9:03 pm

Re: Charging to 80% capacity

eNate wrote: Sun May 15, 2022 1:06 pm Likewise, even BMW with their new i4 and iX is providing an 80% suggestion, plus charge limiting, and even current limiting.
On all the products I sell, I advise people to put them in a hermetically sealed box and never use them. It really cuts down on my warranty costs.

I'm pretty convinced BMW is actively trying to NOT sell any more EVs than they have to at this point.
eNate
Posts: 921
Joined: Mon Sep 09, 2019 5:33 pm

Re: Charging to 80% capacity

Touché!

I speculate BMW can't retroactively introduce charge limiting into i3 software because it would open them up to a whole bunch of claims. So they'd rather stay mum on the matter and move on to the next...
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agzand
Posts: 98
Joined: Tue Dec 22, 2020 3:00 pm

Re: Charging to 80% capacity

3pete wrote: Tue May 17, 2022 1:54 pm
agzand wrote: Mon May 16, 2022 10:13 am BMW came up with departure time charging scheme for the i3, the hope is that you won't let the car sit at 100% charge for extended periods. If you charge to 100% using departure time, it is OK. The problems arise when you charge to 100% and the car sits for a few days, or weeks.
Departure time charging scheme? When was this introduced and how do you get to it?

Are you saying it allows you to tell the car you're leaving at 7am tomorrow and it will charge to 80% immediately then wait to charge the rest of the way so it hits 100% at 7am?

I have only ever noticed the departure time to impact:
1) Battery conditioning overnight and pre-departure
2) Cabin pre-heating or cooling pre-departure
3) A notification that your car will not be charged to 100% if your departure time does not allow enough charging time.
It has been on all i3s from the beginning. I guess your are charging on a low amp charger. If you have a high power charger, the car will calculate when it needs to start charging to get to 100% just before your departure time. The idea is to minimize the time the car spends at 100%.

When you plug in the car, it will do a quick charge to measure how much the charger can deliver. Based on that number it will schedule charging to start at appropriate time. If you want to charge to 80% instead of 100%, you can set your departure time 30 min or 2 hours (based on your charger power) later than your actual departure time.

Again this is all a moot point if your charger cannot deliver enough energy to fill the battery by departure time.
3pete
Posts: 206
Joined: Tue Mar 19, 2019 9:03 pm

Re: Charging to 80% capacity

eNate wrote: Tue May 17, 2022 2:18 pm I speculate BMW can't retroactively introduce charge limiting into i3 software because it would open them up to a whole bunch of claims. So they'd rather stay mum on the matter and move on to the next...
That seems logical and it does fit with how other manufacturers have altered the available battery capacity even after a car leaves the dealer's lot. I think your other point is spot-on that the technology is still so new that manufacturers don't even know for sure what the best approach is so they resort to generalized guidance around batteries that seems to fit, or they err on the side of caution.

It does seem interesting how few i3s have fallen below the warranty threshold based on internet anecdotes and what BMW has claimed. i3 owners probably skew towards early adopters, willing to deal with the quirks of the car and possibly choose to try to manage battery longevity on their own but still I'd think there'd be some solid evidence if particular habits were *definitely* off-limits for battery life.
3pete
Posts: 206
Joined: Tue Mar 19, 2019 9:03 pm

Re: Charging to 80% capacity

agzand wrote: Tue May 17, 2022 2:37 pm It has been on all i3s from the beginning. I guess your are charging on a low amp charger. If you have a high power charger, the car will calculate when it needs to start charging to get to 100% just before your departure time. The idea is to minimize the time the car spends at 100%.

When you plug in the car, it will do a quick charge to measure how much the charger can deliver. Based on that number it will schedule charging to start at appropriate time. If you want to charge to 80% instead of 100%, you can set your departure time 30 min or 2 hours (based on your charger power) later than your actual departure time.

Again this is all a moot point if your charger cannot deliver enough energy to fill the battery by departure time.
Is this part of the "low cost charging" functionality? That's about the only setting I haven't played around with because I don't have TOU rates, so have no need.

My L2 EVSE is capable of 40amps but the i3 only pulls 32. And it definitely charges to 100% as soon as it can, even if I have a departure time set.

How do you get charging to behave the way you're describing?

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