Charging to 80% capacity

[eNate]

I recall reading fairly convincing proof (from the archives, here in this forum) cell balancing occurs at lower states of charge.

But because balancing relies on voltage, it's most effective at high SOCs where there's a meaningful difference between hundredths of a point, where for mid SOCs it's pretty flat.

[alex29a]

I constantly keep my ( now 37000 miles ) 94Ah ( Rex ) Charged up to 100% using the slow home 10A granny charger
as soon as I have used 30-40 miles and the % falls to around 68-70% , it's on charge for around 4-5 hours

I am happy with that, having peace of mind full range.
So far the battery behaviour has been consistant on all the usage/charge readings.
showing no sign of degradation.

I have also left it sitting 100% fully charged for 15 Days when was on holiday.
No effect on anything

Perhaps ?? is it becase a slow charge has less harmful effect on the battery
than fast charge ..? if anyone can comment of that

[alohart]

So far the battery behaviour has been consistant on all the usage/charge readings. showing no sign of degradation.

Noticing mild degradation can be difficult. The free mi3 app (iOS) or electrified app (Android) reports the battery pack state of health which is probably a better indication of degradation than trying to associate usable battery capacity with range that fluctuates with temperature, driving conditions, tire inflation pressure, and several other factors.

I have also left it sitting 100% fully charged for 15 Days when was on holiday. No effect on anything

Maybe, maybe not. 15 days isn't terribly long, but the effects could take a while to be noticeable. BMW warns about leaving the charge level too low, but doing so would likely not be immediately noticeable. Degradation occurs slowly over time, so for those who want to minimize degradation, it's best to avoid doing things that experts advise against.

Perhaps ?? is it becase a slow charge has less harmful effect on the battery
than fast charge ..? if anyone can comment of that

1 C is the charging power that would charge a battery pack from 0% to 100% in 1 hour. 240 VAC Level 2 charging at 30 A (7.2 kW) isn't fast (only 0.22 C for your 33 kWh battery pack). It's probably no worse than 120 VAC Level 1 charging at 10 A (1.2 kW or 0.04 C). DC fast charging (50 kW or 1.5 C) might be more harmful than AC Levels 1 or 2 charging, but those who have looked for evidence of this haven't found much. Other EV's charge at C rates greater than the i3 yet don't suffer much battery cell degradation. If one charged only using DC fast chargers, degradation might be greater over several years than had one charged at AC Levels 1 or 2.

[Gonville]

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%.

No I don’t mean that. The latest i3 manual and the latest Mini SE manuals both say don’t leave it plugged in for long periods and don’t charge past 80%. There are no tools true.

Our view is that it means on DC due to charge rate decline rather than AC but that isn’t clear.

[Gonville]

So? 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.
[/quote]

I don’t agree. The battery experts at battery university are nearly always taking about single cell systems in a laboratory with no thermal management and 1C charge and discharge rates. We are talking about a multi cell with active thermal management system and specific charge buffer allocations. Engineer versus Chemistry. Expert engineers versus expert chemists/physicists.

Nothing we can do about the 1-2% calendar degradation.

As an aside in the U.K. our group with 6,000 members has had only 1 60Ah vehicle have a failed cell replaced under warranty. No 70% battery capacity warranty claims. I think the USA has higher overall temperatures environment and that is an issue I guess.

[VirginiaHershberger]

Thanks for the suggestions. By the way, I need a site where I can find a bridal salon business plan. I hope I will find it soon.

[johnnyz383]

I installed electrify and found out some very interesting things about my pack. I have 6 years experience building lithium packs and know a thing about these cells. My 2015 i3 with 72000 kms had a KAPPA reading of anywhere from 16.2 to 14.9. I also noticed after a dealer update that the pack would seemingly lose percentage without the car doing anything. After initializing the electrified app I found that 1) The battery is 100% solid. 2) The cell balance was within a tenth of a volt. 3) At 100% state of charge (What the BMS is reporting) the pack is at 4.1 volts per cell, and at 20% the pack is only at 3.76 volts!. 4) There is a .5 of amp residual draw even with the car off. 5) I can now ascertain that the pack has MORE capacity than the BMS is reporting, even when you factor in the unusable upper and lower capacity. Time to see if the BMS can be reset, as it appears the BMS is taking into account time and artificially deflating the degredation of the pack. Simply absurd.

[alohart]

Older versions of BMW’s ISTA+ software support initializing the BMS. It must be installed on a Windows laptop and connected to the OBD port with an Ethernet cable that can be purchased online (WiFi and Bluetooth not supported). I don’t have any experience with ISTA+, but several mostly European i3 owners have reported some success at increasing the battery pack’s usable capacity, at least for a few months until the BMS is initialized again. I chose not to try this until my battery pack warranty expired.