Battery range dropping fast

alohart · 2024-11-27T15:50:18-0600

drcarrera said:
If you know roughly when it'll reach your desired charge level can you not just set the appropriate charge window in the app?

I don't think that this would work because the i3's charge window algorithm emphasizes reaching a full charge by the departure time even if this means starting charging prior to the start of the charge window and/or ending charging after the end of the charge window. This behavior has frustrated i3 owners whose priority is to charge only during the presumably low-cost charge window.

drcarrera · 2024-11-28T03:50:05-0600

alohart said:
I don't think that this would work because the i3's charge window algorithm emphasizes reaching a full charge by the departure time even if this means starting charging prior to the start of the charge window and/or ending charging after the end of the charge window. This behavior has frustrated i3 owners whose priority is to charge only during the presumably low-cost charge window.

I set my departure time 5-7 days in the future and then it works fine, although of course this means changing it every couple of days if you're charging regularly. A bigger frustration for me is only having one charging window as we have three cheap periods on our tariff.

DuploCar · 2024-11-28T04:37:53-0600

Best practice seems to depend on battery type
NMC vs LFP
According to this YouTube based on scientific sources (se at the bottom)

In short:
Best practice for the NMC is to charge often and keep charge between 75%
Only charge to 100% when needed, try and use it as soon as it is finished charging.

Caveat: I dont know the battery type from 1014-2017. In 2018 it should be an NMC.

Video sources:
NMC Edition

His sceintific sources:
Lithium Ion Degradation:
- https://pubs.rsc.org/en/content/artic...

Li-Ion Life Cycle Study:
- https://www.sciencedirect.com/science...

Dr. Jeff Dahn:
- https://www.dal.ca/diff/dahn/people/j...

Gonville · 2024-11-28T06:36:52-0600

alohart said:
In September, 2016, British i3 owner Bev Brown was given a workshop tour of the BMW UK HQ where a BMW employee, "The Professor", explained i3 battery cell charge level balancing. "The Professor" said that the charge level "just needs to be above 80% to get the in-car cell balancing active." Cell balancing occurs when the HV system is sleeping (i.e., when the HV battery pack isn't connected to the HV circuit, so not while driving or charging). "It doesn’t matter if you regularly do small top up charges to 60% or not. The very clever BMW Battery Management System (BMS) takes care of it all for you, just so long as you let it have a [80%+] charge regularly" and then "let it have a long, restorative sleep." It's not necessary to leave an EVSE plugged in.

That's been my experience over 10 years of i3 ownership during which I routinely charged our i3's to a displayed 80%-90% charge level unless I might need full range soon. Occasionally displaying BMS data with the mi3 app showed that the minimum and maximum voltages of all 96 battery cells were always within 0.01V at a full charge indicating excellent charge level balance even without routinely charging to 100%.

I was at that meeting and pictures from it are in David Bricknell’s excellent book. Bev was the lead admin on our group until she moved to a Polestar.

I think the main lesson is not just to go ‘above 80%’ but to let the BMS do its thing. Arbitrarily stopping it thinking you are improving battery life is a bit false.

The one main message should be :-

‘Do not be afraid to charge to 100%’

There is some chat from others at that meeting that he said “…at least 80%” and others have hit on 84% for the exact algorithm. Trouble is that was at 60Ah days and the mix is different for the 3 packs. Top and bottom reserves I mean.