Failing 12V or Converter issue?

[alohart]

Speaking with a friend who has had an i3, he thinks that one or more of the battery cells/modules may be bad.

I've called up BMW and they want ~$1k to update the software and run an HV diagnostic. My 1 week old i3 is already becoming a money pit.

Does anybody on Oahu have an independent shop that they would use for diagnostic and/or module replacement that they could recommend?
(pics all taken 24hrs apart from each other, 48hrs in total)

One or more very weak cells could be the cause, I suppose. However, your i3's battery pack warranty has expired, so even if BMW of Honolulu returned a diagnosis of a bad module (individual battery cells cannot be replaced, only 12-cell modules), you would have to pay for a repair which would almost certainly be a complete battery pack. Replacing a bad module wouldn't be a good repair because its cells would have different capacities from cells in the other 7 modules resulting in a poorly performing battery pack. The cost of a new battery pack would far exceed the value of your i3.

I have a smartphone app that could display the minimum and maximum cell voltages, temperatures, charge levels, and capacities which should detect whether at least 1 cell is weak. I live in Hawaii Kai. Send me private message ("Start conversation") if you would like to have this app display info about your battery pack.

However, the best solution would be to return your i3 to the seller for a full refund.

 

[EdG]

Thank you Alohart, PM sent!

Quick update to add today's report, 0.5% down, though range up. A drastic change from the 25% lost the other day, and 4.5% the day prior.

Will keep on it daily if possible to document the decreases

 

[EdG]

As an update (and thank you Alohart for your assistance) we have:
100% fully charged
87% after 9 miles
52.5% after 18 miles
Clearly something isn't right with either the battery, or reporting of SOC

At this rate, the car has a range of maybe 30mi or less, though the max kappa showed 14.6kw last week and 13.5kw yesterday

 

[alohart]

I scanned EdG's very nice i3 with mi3 and BimmerLink. Its displayed charge level was 100% showing 64 miles of predicted Comfort mode range with the A/C on, so not unreasonable for a 60 Ah battery pack that has degraded 20-25% over 45k miles and 10 years. The minimum and maximum cell voltages, charge levels, and temperatures were all very close indicated good cell charge level balance. The minimum and maximum estimated cell capacities varied by ~3 Ah which is a bit higher than I've seen with any of our i3's, but not crazy high. Things might look different at a low charge level.

BimmerLink offered to scan only 6 to 8 electronic modules compared with 26 on our 2021 i3. Why would this be so different? There weren't a crazy number of DTC's stored in error or info memory, and maybe only 1 DTC in the instrument panel that was permanent (can't recall for certain). BimmerLink was able to erase almost all DTC's which nothing suspicious remaining.

I had hoped that a fairly recent 12V battery replacement might have resulted in spurious DTC's being stored and maybe resulting in unexpected behaviors and that erasing them might have fixed this phantom HV battery pack discharge problem. Unfortunately, it didn't.

One explanation would be that something is preventing the HV system from shutting down normally so that it is always on discharging the HV battery pack. If the HV disconnect were disconnected, the HV battery contractors would open which would prevent HV loads from discharging the battery pack. However, if one or more battery cells is failing and somehow discharging the entire battery pack, this would still occur with the HV disconnect disconnected. Does that seem like something worthwhile to try?

A wrinkle to this story is that the new owner of this i3 lives overseas and apparently bought this i3 remotely to use during occasional visits. A friend is storing it for him but didn't sign on to help fix problems, and I'm just a guy who lives within 10 miles of the friend and offered to help. I would probably try a few things myself if this were my i3, but no one expects the friend with a full-time job and family to spend much time on this.

So any suggestions would be very welcome!