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      01-05-2021, 04:15 AM   #23
Leto1701
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Quote:
Originally Posted by MolarBear View Post
My local dealership (Leeds, UK) tested the batteries for me. It involved discharging and recharging the batteries - they printed an extensive report with a load of figures with voltages of each of the cells and different figures. All within range although annoyingly despite the low age and mileage (20 months or so, and 7000 miles) it was at 91%.
LiIon batteries don't age in a linear way. They loose some capacity quickly in the beginning and then the curve goes pretty flat. So I wouldn't worry about 91%. That might now hardly change for a couple years. This is how both my Tesla batteries behaved (before Tesla started to limit charging speed and power output for aging batteries to circumvent their own warranty).
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      01-05-2021, 04:25 AM   #24
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I know for a fact the BMW dealership left the car go flat for 8 months over lockdown in a car park without plugging it in before the sale. I suspect this might have something to do with it!
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      01-05-2021, 08:13 AM   #25
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Originally Posted by MolarBear View Post
I know for a fact the BMW dealership left the car go flat for 8 months over lockdown in a car park without plugging it in before the sale. I suspect this might have something to do with it!
The batteries don't go flat, at 0% there is a save charge level still in the battery. However, 8 months is a long time. It won't have helped the battery life. If fully charged before it might have just survived before turning into a brick. Wouldn't have bought it to be honest. 91% still sounds O.K. for the cells. The exposed "window" however should have hidden that from you. 91% visible would be O.K. for a Tesla (they allow full capacity use up to max. Voltage to advertise higher kWh and range). For BMWs more conservative strategy it is a concern.
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      01-05-2021, 09:30 AM   #26
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Originally Posted by MolarBear View Post
I know for a fact the BMW dealership left the car go flat for 8 months over lockdown in a car park without plugging it in before the sale. I suspect this might have something to do with it!
There are explicit instructions from BMW according to which the i8 should be recharged every 6 weeks in the event of longer periods of inactivity.

"No. 61 03 98 (387) Battery recharging intervals for stationary vehicles, battery charging calendar and battery hangers (12 V battery, high-voltage battery unit)"

Including a "BMW Battery Calendar" for non US models and a "Battery Log Form" for US models.
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      01-07-2021, 07:03 PM   #27
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Quote:
Originally Posted by Leto1701 View Post
LiIon batteries don't age in a linear way. They loose some capacity quickly in the beginning and then the curve goes pretty flat. So I wouldn't worry about 91%. That might now hardly change for a couple years. This is how both my Tesla batteries behaved (before Tesla started to limit charging speed and power output for aging batteries to circumvent their own warranty).
Exactly.
Interestingly, my 2014 i8 with 70k mi is still at 100%, while the same old i3 with 30k mi is now at 93%.Different types of stress of course.
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      01-11-2021, 03:45 PM   #28
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Originally Posted by BigT View Post
Exactly.
Interestingly, my 2014 i8 with 70k mi is still at 100%, while the same old i3 with 30k mi is now at 93%.Different types of stress of course.
Much higher stress on i8 battery btw, but they are designed differently to accomodate that.

However leaving a car to go flat over 8 months can't have done it any good.
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      01-18-2021, 07:29 PM   #29
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Originally Posted by JasH View Post
Much higher stress on i8 battery btw, but they are designed differently to accomodate that.
Frankly, I don't know enough about that, but at least the i8 doesn't allow the demanding 50kW fast charging, which is known as one major degradation factor.

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However leaving a car to go flat over 8 months can't have done it any good.
Yes, whoever allows something like this is a bit stupid and has only himself to blame or the pre owner.
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      01-20-2021, 03:27 AM   #30
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Originally Posted by JasH View Post
Much higher stress on i8 battery btw, but they are designed differently to accomodate that.

However leaving a car to go flat over 8 months can't have done it any good.
It doesn't matter only how fast you charge regarding stress. It matters at which proportion of the capacity per time you charge. For the about 10 kWh of the current i8 battery the about 2,3kW charge is 0,23C. If you have a 100 kWh battery, you can charge at 22kW with the same stress on the battery. 1C is perfectly fine as charging speed. For the 43 kWh i3, 50 kW is just over 1C and no issue. Charging an i8 at 5C (50 kW) or more would. That's also why Tesla doesn't charge at more than 1C at the superchargers anymore for most of the time, no matter what kW they advertise. The Cells can't take it. At the moment, Porsche leads the pack there with what sustained charging speed the cells can take. If they will last we will see...
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      01-21-2021, 04:41 PM   #31
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It doesn't matter only how fast you charge regarding stress.
I didn't say anything about charging causing stress.
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      01-25-2021, 04:34 AM   #32
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I didn't say anything about charging causing stress.
Well it does. The i8 charges at max. 60 kW recuperating. That is 6C or something. Just something to be aware of. Taking 10C out of the battery is not an issue, if it isn't too cold. Those BMSes have a lot of parameters to keep in mind
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      01-30-2021, 07:29 PM   #33
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Quote:
Originally Posted by Leto1701 View Post
Well it does. The i8 charges at max. 60 kW recuperating. That is 6C or something. Just something to be aware of. Taking 10C out of the battery is not an issue, if it isn't too cold. Those BMSes have a lot of parameters to keep in mind
That isn't sustained though, there is a difference between regen or acceleration for 5-10 seconds versus charging for 30 minutes
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      02-01-2021, 06:25 AM   #34
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That isn't sustained though, there is a difference between regen or acceleration for 5-10 seconds versus charging for 30 minutes
It can be on long slopes. Just something to be aware of.
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      02-01-2021, 05:23 PM   #35
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Quote:
Originally Posted by Leto1701 View Post
Well it does. The i8 charges at max. 60 kW recuperating. That is 6C or something. Just something to be aware of. Taking 10C out of the battery is not an issue, if it isn't too cold. Those BMSes have a lot of parameters to keep in mind
It is really 60kW of regen? That's actually much better than I expected, my dual motor Tesla gets 72kW max regen and it's hard to get a feel for the full regen in the i8, since you have to apply the brakes and can't really feel what is regen or friction braking.
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      02-01-2021, 07:40 PM   #36
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Speaking of batteries and charge. My 2018 LCI i8 coupe intermittently gives the error ' Drivetrain. No restart'. The associated OBD2 code was 1D3702 Power Management, Battery: Faulty Charge By High-Volt Battery ( among others like Standby Current Violation) Then sometime the error spontaneously disappears and the car drives perfectly and can restart. Pat (Patonlinegarage) ,ever so kindly, suggested I consider the 12v battery . I just did a load test and the battery readings are ok with a state of health at 91%. Can it still be the 12v causing the error if all the measurements during battery testing seem fine? My car was bought in the UK and still under warranty but I shipped it to Trinidad and the local agents refuse to touch it.

Last edited by necropsyblade; 02-01-2021 at 07:45 PM.. Reason: add info
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