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!

 

[weajd]

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.

This sounds logical to me. Check the state of charge (SOC1). Isolate the battery. Let sit for a few days. Reconnect HV disconnect. Check the state of charge (SOC2). Compare SOC1 and SOC2. It is not going to isolate which module. If no charge loss, the remote friend may want to always disconnect the HV (12v) when he leaves HI and reconnect them and recharge both when he returns.

Otherwise, someone with the ITSA software, computer and connector hardware would be in a better position to check out the HV battery and other components that may be draining current from the HV and/or 12v battery.

Kudos to you trying to help on this.

 

[EdG]

Thanks for all of the help, and the suggestion to disconnect the HV makes sense. That said, it may be more than my friend can take on at the moment, so I think we're back to just keeping an eye on things.

Attached are photos taken 3hrs apart, showing that the car hasn't moved, but we're still losing 7% anyway. Thankfully it seems to hold on better now, not losing drastic amounts of power overnight when not in use. I've asked my friend to just let it sit a few days and monitor daily to see the trend.

 

[EdG]

Here's the result today after a bit of driving. Another 20% loss overnight

 

[mojo]

One test that might be interesting and easy to do: Does the Hazard Warning switch backlight go off after the standard period? As I understand it, on any "normal" i3, this will stay on for ~12 minutes after the car is turned off and the last door shut, and should then go out (any action such as opening a door will reset the 13 minute period timer). The light going out indicates that the car has entered it's lowest-power "sleep" state.

I don't think it would be possible for the HV battery to still be connected to the rest of the car when it's in lowest-power state.