Rotten Eggs smells and a hot 12-volt battery

[wegogo]

Not normally. However, the Intelligent Battery Sensor (IBS) in the 12V battery's negative cable clamp sends voltage, charge and discharge current, and temperature measurements every 14 seconds to the Electrical Digital Motor Electronics (EDME) via a data bus. Under conditions apparently undocumented to the public (low voltage?), the EDME orders the DC-DC converter to charge the 12V battery for 1 hour, then stops the charging while it continues monitoring the 12V battery. BMW has been installing the IBS in its vehicles for years, so its power management seems as good or better than that implemented by many auto manufacturers.

If the battery was hot, its elevated temperature would have been noticed by the EDME. I don't know what the EDME would do with these data, but it would make sense that it would prevent the 12V battery from being charged even if its voltage were below normal.

The LFP battery in our i3 includes a Bluetooth radio that communicates with a smartphone app that supports disabling/enabling charging and the display of current battery data. Its app reports a charging current of ~50A when the battery's charge level is fairly low, I enable its charging, and the DC-DC converter is on. I don't know whether the DC-DC converter is limiting the charging current or whether the battery's internal resistance is. 50A increases the battery cell temperature by several degrees over a short time period, but the EDME hasn't stopped the charging, so this must be within its safe limits. The battery itself reports an overcurrent condition if the charging current exceeds 100A.

You might be making an incorrect assumption that your battery's outgassing was caused by it being charged by the DC-DC converter when it was failing. A 12V lead-acid battery with an internal short circuit could produce hydrogen sulfide and hydrogen gasses while in thermal runaway even when it's not being charged. All i3's have advanced power management that monitors the 12V battery and is designed to do the right thing under a variety of circumstances, so it's unlikely that the DC-DC converter was continuously charging your hot, failing 12V battery.

Again, you're assuming that your battery was outgassing because it was being charged recklessly by your i3. I think that this is highly unlikely and that there's nothing to issue a recall about. You just got unlucky to have a 12V battery that probably suffered an internal short circuit, entered thermal runaway, got hot, and outgassed. This is a fairly common 12V battery failure mode. It's why BMW installed a vent tube on the i3's 12V battery. However, if it is venting into a closed garage, there's nothing that an i3's software could do to prevent an accumulation of poisonous and flammable gasses in your garage and eventually in your house.

If the EDME sensed a hot battery, it would have been nice if it could have relayed this info to BMW's servers so that they could have sent you an email message like they do when charging initiates, completes, or is unexpectedly interrupted, or maybe relayed that info to your My BMW app which could have produced a push notification on your phone. While BMW seems to be pretty advanced in some ways, its software isn't as powerful as it could be.

Mine is a 2016, so I don't believe I get access to the internet enabled data features you mentioned. I plan to get the multimeter out and see what I can find out about the charging. I bought the car earlier this year. It has a BMW battery marked 09/22, failed 3 months out from 2 year warranty. Not only that - the BMW advisor told me if I don't have a receipt for it, they wouldn't have replaced it anyway. Refusal to honor warranty from previous owner ... They want $375 + labor for a 12v battery - hilarious.

The problem was first noticed while the i3 had been charging for several hours, which I believe is when the i3 attempts to keep the 12v system charged, in addition to running mode. I unplugged the i3, and parked it outside. The battery cooled and smell was gone, so I brought it back in - no smell accumulation. If I understand your doubt of my assumptions, plugging the i3 back in to charge will not make the battery outgas again, because it was probably just the battery going through failure and the i3's system will recognize a problem and stop charging it?

My guess right now is that if I can measure it without the HV system trying to charge it, it will read something like 11 volts, and when I plug the i3 in, the system will try to charge it, which will apply 14-15 volts to the battery. Then, if I let it charge for a couple hours it will get very hot and start smelling of sulfur again.


The most likely problem, is that the car sat at the dealer, the new 12v discharged almost all the way, then when the car was test driven/plugged in, it overcharged/charged too fast. This is very common with ICE cars as well...the alternator doesn't know the battery is dead and needs a nice slow charge. If you try to charge with full current based on the internatl resistance, the battery will get up to 'full' voltage before it is really charged all the way. Then it sits for a few hours, voltage drops as the cells equalize, and the overcharging process starts the next time you drive. This is what kills most batteries prematurely. ICE vehicles don't have to do anything about this problem, because your battery probably won't catch on fire in the time you are driving. EV's will need to be more careful, and probably usually are. My car likely has old software...if I express my concerns of safety to BMW, do you think they will update it for free?


I have owned many cars, and have encountered many failed batteries - and even those that have failed cells or some other full failure mode where they cannot hold a charge for 1 day, I have never had a single one outgas to the extent happening here. I have a simple shumacher battery charger that cost $40 from 2012 or so, and it is able to charge a battery indefinitely without allowing it to overheat and gas this much - yes, even failed batteries.

 

[Mondomensch]

Mine is a 2016, so I don't believe I get access to the internet enabled data features you mentioned. I plan to get the multimeter out and see what I can find out about the charging. I bought the car earlier this year. It has a BMW battery marked 09/22, failed 3 months out from 2 year warranty. Not only that - the BMW advisor told me if I don't have a receipt for it, they wouldn't have replaced it anyway. Refusal to honor warranty from previous owner ... They want $375 + labor for a 12v battery - hilarious.

The problem was first noticed while the i3 had been charging for several hours, which I believe is when the i3 attempts to keep the 12v system charged, in addition to running mode. I unplugged the i3, and parked it outside. The battery cooled and smell was gone, so I brought it back in - no smell accumulation. If I understand your doubt of my assumptions, plugging the i3 back in to charge will not make the battery outgas again, because it was probably just the battery going through failure and the i3's system will recognize a problem and stop charging it?

My guess right now is that if I can measure it without the HV system trying to charge it, it will read something like 11 volts, and when I plug the i3 in, the system will try to charge it, which will apply 14-15 volts to the battery. Then, if I let it charge for a couple hours it will get very hot and start smelling of sulfur again.


The most likely problem, is that the car sat at the dealer, the new 12v discharged almost all the way, then when the car was test driven/plugged in, it overcharged/charged too fast. This is very common with ICE cars as well...the alternator doesn't know the battery is dead and needs a nice slow charge. If you try to charge with full current based on the internatl resistance, the battery will get up to 'full' voltage before it is really charged all the way. Then it sits for a few hours, voltage drops as the cells equalize, and the overcharging process starts the next time you drive. This is what kills most batteries prematurely. ICE vehicles don't have to do anything about this problem, because your battery probably won't catch on fire in the time you are driving. EV's will need to be more careful, and probably usually are. My car likely has old software...if I express my concerns of safety to BMW, do you think they will update it for free?


I have owned many cars, and have encountered many failed batteries - and even those that have failed cells or some other full failure mode where they cannot hold a charge for 1 day, I have never had a single one outgas to the extent happening here. I have a simple shumacher battery charger that cost $40 from 2012 or so, and it is able to charge a battery indefinitely without allowing it to overheat and gas this much - yes, even failed batteries.

My local dealer charges $540 flat rate for new 12V battery, installed, in any model bmw.

Apparently as reported here and elsewhere, getting the oem model battery with venting tube runs about $250; given the presumed damage to your current battery, wouldn’t it make sense to just replace it? Not sure if I missed something here - the thread is lengthening.

 

[wegogo]

My local dealer charges $540 flat rate for new 12V battery, installed, in any model bmw.

Apparently as reported here and elsewhere, getting the oem model battery with venting tube runs about $250; given the presumed damage to your current battery, wouldn’t it make sense to just replace it? Not sure if I missed something here - the thread is lengthening.

I've ordered one from batteries plus who had an equivalent for about $150.

My issue, and the reason I added to the thread, is that it appears the i3 is overcharging batteries that are in failure leading to realease of poisonous and possibly explosive gas. This is happening in a completely expected, yet dangerous situation, closed garage while charging.

There is nothing in the required maintenance about replacing the 12v battery preemptively every 2 years to prevent fire/death.

I think if you purchased a battery charger/maintainer and placed it on your car battery, you would expect it to stop charging at a high rate so as to prevent gassing and fire hazard. If it were to not stop, you might expect the product to be recalled, at least under modern conventions.

 

[Mondomensch]

Gotcha. If you haven't already, perhaps consider filing a complaint with the NHTSA.

 

[wegogo]

I wrote about a similar experience – burned oder followed by a failed 12 volt battery – in March of last year. The battery was roughly 1½ years old.

I chalked it up to a defective battery, nothing wrong with the car. BMW swapped it out and it's been problem-free since.

https://www.mybmwi3.com/threads/odd...w-12v-batt-or-heater-precon.18003/#post-72973

Not normally. However, the Intelligent Battery Sensor (IBS) in the 12V battery's negative cable clamp sends voltage, charge and discharge current, and temperature measurements every 14 seconds to the Electrical Digital Motor Electronics (EDME) via a data bus. Under conditions apparently undocumented to the public (low voltage?), the EDME orders the DC-DC converter to charge the 12V battery for 1 hour, then stops the charging while it continues monitoring the 12V battery. BMW has been installing the IBS in its vehicles for years, so its power management seems as good or better than that implemented by many auto manufacturers.

If the battery was hot, its elevated temperature would have been noticed by the EDME. I don't know what the EDME would do with these data, but it would make sense that it would prevent the 12V battery from being charged even if its voltage were below normal.

The LFP battery in our i3 includes a Bluetooth radio that communicates with a smartphone app that supports disabling/enabling charging and the display of current battery data. Its app reports a charging current of ~50A when the battery's charge level is fairly low, I enable its charging, and the DC-DC converter is on. I don't know whether the DC-DC converter is limiting the charging current or whether the battery's internal resistance is. 50A increases the battery cell temperature by several degrees over a short time period, but the EDME hasn't stopped the charging, so this must be within its safe limits. The battery itself reports an overcurrent condition if the charging current exceeds 100A.

You might be making an incorrect assumption that your battery's outgassing was caused by it being charged by the DC-DC converter when it was failing. A 12V lead-acid battery with an internal short circuit could produce hydrogen sulfide and hydrogen gasses while in thermal runaway even when it's not being charged. All i3's have advanced power management that monitors the 12V battery and is designed to do the right thing under a variety of circumstances, so it's unlikely that the DC-DC converter was continuously charging your hot, failing 12V battery.

Again, you're assuming that your battery was outgassing because it was being charged recklessly by your i3. I think that this is highly unlikely and that there's nothing to issue a recall about. You just got unlucky to have a 12V battery that probably suffered an internal short circuit, entered thermal runaway, got hot, and outgassed. This is a fairly common 12V battery failure mode. It's why BMW installed a vent tube on the i3's 12V battery. However, if it is venting into a closed garage, there's nothing that an i3's software could do to prevent an accumulation of poisonous and flammable gasses in your garage and eventually in your house.

If the EDME sensed a hot battery, it would have been nice if it could have relayed this info to BMW's servers so that they could have sent you an email message like they do when charging initiates, completes, or is unexpectedly interrupted, or maybe relayed that info to your My BMW app which could have produced a push notification on your phone. While BMW seems to be pretty advanced in some ways, its software isn't as powerful as it could be.

I have plugged the car back in. Before I did so, I measured voltage at the battery, and as you noted in a different thread, as soon as you unlock/open a door, it starts attempting to run the DC-DC system, applying 14.8V to the battery. Plugged in, it measures the same. I opened up bimmerlink, and watched the battery state go to 99%, where it remains stuck - I do not think it will ever read 100%. The DC-DC system continues to shove out 14.6+V. This is charging with doors locked. The battery first gets hot on one side, then gets hot all over as it is having quite a bit of current pushed through it, with no chemical reaction to make since the battery is fully charged, it will only make 100's (or 1000's) of watts of heat inside the battery. The sulfur smell is accumulating again. Though not as strong as when it had been charging for hours, I am not going to let it build up that much again, so I opened the garage while I continue testing. Now even with the door opened, the smell is getting stronger. This is not surprising because the i3 is applying rapid charging voltage to a fully charged battery.

I am now 100% certain the i3 is recklessly charging the 12v battery. The i3 is treating it's 12v system like an ICE vehicle driving down the road at half throttle and load, in every situation the DC-DC system is on. Even with a fully charged 12v battery. This is a dangerous problem. This is an obvious programming defect and should be remedied for safety.

For comparison, I hooked up a basic battery charger to my 750 - also an BMW AGM 12v battery. It read the battery at 12.4V, 63% charge state. It began charging at 12.6V and slowly increased the voltage to 13.5V. As the battery warms and cools, the voltage fluctuates between 13.0 and 13.5. This is proper charging of a battery. What the i3 is doing (at least in model year 2016) is not.

These batteries are meant to have a service life of 10 years, so it astounds me to see people saying just replace it and move on. It should be obvious there is a problem.

What I am now curious about: will replacing the battery cause the charging system to behave differently? Is it in some sort of fail-state where it thinks it needs to pump out 14.6V to keep electronics going without a good 12 battery? Or does the system always charge like this and slowly ruin batteries for people who charge every day?

 

[alohart]

Mine is a 2016, so I don't believe I get access to the internet enabled data features you mentioned.

Correct.

I plan to get the multimeter out and see what I can find out about the charging.

You'll need to pop the frunk lid (hood) which will turn on the HV system. Then wait ~30 minutes without locking/unlocking the doors or hatch for the HV system to shut down. Only then would you be able to measure the voltage of the 12V battery, but this probably won't be its resting voltage for several hours.

The problem was first noticed while the i3 had been charging for several hours, which I believe is when the i3 attempts to keep the 12v system charged, in addition to running mode.

Correct. Except that when the 12V battery is fully charged, the DC-DC converter turns off, maybe unless 12V components are consuming more than a certain amount of power.

If I understand your doubt of my assumptions, plugging the i3 back in to charge will not make the battery outgas again, because it was probably just the battery going through failure and the i3's system will recognize a problem and stop charging it?

The Electric Motor Digital Electronics (EDME) module knows the 12V battery's voltage, current flow, and negative terminal temperature, but not the temperature inside the battery. I assume that the negative terminal would heat up eventually as well. However, I have no idea what the EDME considers dangerous 12V battery conditions. A hot negative terminal would seem to be a candidate as well as a really high current.

EV's will need to be more careful, and probably usually are. My car likely has old software...if I express my concerns of safety to BMW, do you think they will update it for free?

The Intelligent Battery System (IBS) has been available on BMW's for more than a decade, and battery failures like the one you experienced are not new, so I doubt that BMW has updated its IBS software to deal with this failure situation since the i3 was released a decade ago. I've read no reports of 12V battery fires in i3's, so this doesn't seem to be a common problem that would have been addressed in a system software update (a.k.a., integration level increase). You could certainly try for a free system software update, but a BMW dealer who charges $375 for an i3 battery probably isn't going to do much for free.

You should be able to get a free integration level increase if the current integration level of your i3 is ≥ I001-17-11-500 and < I001-20-03-520. The warranty to cover a sporadic loss of power steering has been extended to 10 years/120,000 miles.

 

[Mondomensch]

I have plugged the car back in. Before I did so, I measured voltage at the battery, and as you noted in a different thread, as soon as you unlock/open a door, it starts attempting to run the DC-DC system, applying 14.8V to the battery. Plugged in, it measures the same. I opened up bimmerlink, and watched the battery state go to 99%, where it remains stuck - I do not think it will ever read 100%. The DC-DC system continues to shove out 14.6+V. This is charging with doors locked. The battery first gets hot on one side, then gets hot all over as it is having quite a bit of current pushed through it, with no chemical reaction to make since the battery is fully charged, it will only make 100's (or 1000's) of watts of heat inside the battery. The sulfur smell is accumulating again. Though not as strong as when it had been charging for hours, I am not going to let it build up that much again, so I opened the garage while I continue testing. Now even with the door opened, the smell is getting stronger. This is not surprising because the i3 is applying rapid charging voltage to a fully charged battery.

I am now 100% certain the i3 is recklessly charging the 12v battery. The i3 is treating it's 12v system like an ICE vehicle driving down the road at half throttle and load, in every situation the DC-DC system is on. Even with a fully charged 12v battery. This is a dangerous problem. This is an obvious programming defect and should be remedied for safety.

For comparison, I hooked up a basic battery charger to my 750 - also an BMW AGM 12v battery. It read the battery at 12.4V, 63% charge state. It began charging at 12.6V and slowly increased the voltage to 13.5V. As the battery warms and cools, the voltage fluctuates between 13.0 and 13.5. This is proper charging of a battery. What the i3 is doing (at least in model year 2016) is not.

These batteries are meant to have a service life of 10 years, so it astounds me to see people saying just replace it and move on. It should be obvious there is a problem.

What I am now curious about: will replacing the battery cause the charging system to behave differently? Is it in some sort of fail-state where it thinks it needs to pump out 14.6V to keep electronics going without a good 12 battery? Or does the system always charge like this and slowly ruin batteries for people who charge every day?

Could it be a failure in your i3's battery management system? Also, presumably at this point at least the battery is damaged and perhaps not behaving normally. My understanding on at least the Optima AGM batteries is that the gas venting ports opening is a one time safety measure to prevent explosion and the battery should no longer be used after that.

 

[wegogo]

Correct.

You'll need to pop the frunk lid (hood) which will turn on the HV system. Then wait ~30 minutes without locking/unlocking the doors or hatch for the HV system to shut down. Only then would you be able to measure the voltage of the 12V battery, but this probably won't be its resting voltage for several hours.

Not too long after locking - maybe 1 hour, 13.2V

Correct. Except that when the 12V battery is fully charged, the DC-DC converter turns off, maybe unless 12V components are consuming more than a certain amount of power.

The DC-DC converter does not seem to be shutting off. It seems to be outputting at its highest voltage for hours with fully charged 12v doors locked, charging HV.

The Electric Motor Digital Electronics (EDME) module knows the 12V battery's voltage, current flow, and negative terminal temperature, but not the temperature inside the battery. I assume that the negative terminal would heat up eventually as well. However, I have no idea what the EDME considers dangerous 12V battery conditions. A hot negative terminal would seem to be a candidate as well as a really high current.

The Intelligent Battery System (IBS) has been available on BMW's for more than a decade, and battery failures like the one you experienced are not new, so I doubt that BMW has updated its IBS software to deal with this failure situation since the i3 was released a decade ago. I've read no reports of 12V battery fires in i3's, so this doesn't seem to be a common problem that would have been addressed in a system software update (a.k.a., integration level increase). You could certainly try for a free system software update, but a BMW dealer who charges $375 for an i3 battery probably isn't going to do much for free.

I have a feeling this is a software issue where it is entering a failsafe to keep the 12V system up as that is used to keep the car on and could be a safety issue if voltage falls below 11 or so volts.

You should be able to get a free integration level increase if the current integration level of your i3 is ≥ I001-17-11-500 and < I001-20-03-520. The warranty to cover a sporadic loss of power steering has been extended to 10 years/120,000 miles.

Thank you! Now that you mention it, I do sporadically feel loss of some steering control sometimes <i-step>I001-18-11-539</i-step>

 

[wegogo]

Could it be a failure in your i3's battery management system? Also, presumably at this point at least the battery is damaged and perhaps not behaving normally. My understanding on at least the Optima AGM batteries is that the gas venting ports opening is a one time safety measure to prevent explosion and the battery should no longer be used after that.

I think so. I think for some reason the software is telling it to give maximum charge to the 12v system. I might try recoding the battery and/or removing the battery and clearing codes to see if the behavior changes before replacing the battery. I'm still waiting on the one I ordered anyhow.

 

[alohart]

I am now 100% certain the i3 is recklessly charging the 12v battery. The i3 is treating it's 12v system like an ICE vehicle driving down the road at half throttle and load, in every situation the DC-DC system is on. Even with a fully charged 12v battery. This is a dangerous problem. This is an obvious programming defect and should be remedied for safety.

If your analysis is correct, this has been happening for over a decade with no reports of 12V battery fires that I've read.

For over 6 years, I've kept a 12V voltmeter in the auxiliary power port beneath the center of the dashboard. The 12V system voltage isn't always 14.0+ volts, so the DC-DC converter is being turned on and off so isn't constantly on. I've never measured a voltage higher than 14.3V, even at the battery terminals, but maybe that's due to our warm ambient temperatures.

These batteries are meant to have a service life of 10 years, so it astounds me to see people saying just replace it and move on. It should be obvious there is a problem.

Only in colder climates have i3 batteries lasted almost 10 years. The original battery in the 2014 that we bought new lasted 7.5 year before its capacity decreased too much to remain usable. However, the original batteries in our used 2019 and 2021 i3 failed after 3.5 years. The batteries have remained the same model for all i3's.

What I am now curious about: will replacing the battery cause the charging system to behave differently? Is it in some sort of fail-state where it thinks it needs to pump out 14.6V to keep electronics going without a good 12 battery? Or does the system always charge like this and slowly ruin batteries for people who charge every day?

Although registering a replacement battery in BMW ICE vehicles apparently does change the charging behavior, it apparently doesn't in i3's.

The low capacity 20 Ah i3 battery probably needs the assistance of the DC-DC converter much of the time an i3 is running to prevent the battery from discharging too much. However, the output voltage of the DC-DC converter could certainly be lower to power 12V components without overcharging the 12V battery. I've not seen its output voltage outside the range of 13.9V to 14.3V.

When I bought a 2000 Honda Insight hybrid in 2002, it was the first car that I had owned that didn't have an alternator and used a DC-DC converter to charge its 32 Ah 12V battery. Its 12V battery failed more quickly than normal. Owners theorized that always being maintained at a full charge with no large discharge from a 12V starter motor led to the early failure. Some owners would purposely discharge the 12V battery periodically by leaving headlights and climate control fans on while parked. I can't recall that this helped extend the life of the battery. However, there might be something to this because the i3 also always maintains its 12V battery at a full charge, no 12V component discharges it much, and the average battery fails prematurely.

I have switched to a LFP 12V battery hoping for longer battery life. This battery wouldn't be suitable for a cold climate because it doesn't include a battery heater like one of these batteries designed for Rivian trucks which also physically fits in an i3 but is much more expensive. Ohmmu batteries include a Bluetooth radio supporting communications with a smartphone running the Ohmmu app. The app supports setting the BMS to disable charging or discharging. By disabling charging, I let the battery's charge level decrease to ~50% before enabling charging to increase the charge level. With a resting voltage ~0.5V higher than the OEM AGM battery, even at a 50% charge level, the output voltage of this LFP battery is greater than a fully-charged AGM battery. I hope that this battery will last longer than the AGM battery.

 

[alohart]

Not too long after locking - maybe 1 hour, 13.2V

That's high for the resting voltage of a fully-charged AGM battery. At 25º C, the resting voltage is ~12.8V.

The DC-DC converter does not seem to be shutting off. It seems to be outputting at its highest voltage for hours with fully charged 12v doors locked, charging HV.

That's not normal behavior. It should shut off when the HV system shuts down within 30 minutes of shutting off an i3. Exceptions would be if HV battery charging is active, the battery pack and/or cabin is being preconditioned, or the voltage of the 12V battery is below a certain level. However, it would stay on to charge the 12V battery for only 1 hour.

 

[wegogo]

That's high for the resting voltage of a fully-charged AGM battery. At 25º C, the resting voltage is ~12.8V.

That's not normal behavior. It should shut off when the HV system shuts down within 30 minutes of shutting off an i3. Exceptions would be if HV battery charging is active, the battery pack and/or cabin is being preconditioned, or the voltage of the 12V battery is below a certain level. However, it would stay on to charge the 12V battery for only 1 hour.

View attachment 1740

Your voltage graph looks like behavior that would make sense for the system to do

Now, I'm looking in bimmercode/bimmerlink and it is getting curiouser and curiouser. Would you happen to be able to check how your battery is coded? On by bimmercode app, there is no option for 20Ah AGM. There is 20 Ah, 40Ah, 40Ah AGM, etc... In bimmerlink, I just registered the same old battery as a new one, and already the charging voltage behavior is different. Immediately, it went down to 14.4V. Then I plugged HV in, and voltage at the 12V battery slowly dropped to 14.1 so far, whereas before re-registering the battery, it would sit at 14.6V for hours.

 

[alohart]

Your voltage graph looks like behavior that would make sense for the system to do

I forgot to mention that this chart was recorded when my 12V battery was failing (insufficient capacity or failure to hold a charge).

Now, I'm looking in bimmercode/bimmerlink and it is getting curiouser and curiouser. Would you happen to be able to check how your battery is coded?

When trying to figure out how to set the battery capacity and type parameters for my 22 Ah LFP battery in BimmerCode, I noticed that there weren't any lithium types and that the AGM type was available only in certain capacities. I chose "40 Ah" to reflect the greater capacity of my LFP battery. I've never noticed any change in the charging behavior when I've made a change to the battery capacity and type, but they I haven't done this much or paid close attention.

On by bimmercode app, there is no option for 20Ah AGM. There is 20 Ah, 40Ah, 40Ah AGM, etc... In bimmerlink, I just registered the same old battery as a new one, and already the charging voltage behavior is different. Immediately, it went down to 14.4V. Then I plugged HV in, and voltage at the 12V battery slowly dropped to 14.1 so far, whereas before re-registering the battery, it would sit at 14.6V for hours.

I don't recall that 20 Ah AGM wasn't a choice. It's probably unlikely that any BMW would have a tiny 20 Ah flooded-cell lead-acid battery, so I assume that "20 Ah" must be the AGM type.

I assume that BimmerLink displayed your battery as a 20 Ah AGM battery before you re-registered it as the same capacity and type so that your battery hadn't been registered incorrectly in the past which might have explained the DC-DC converter behavior. It's very interesting that the charging behavior changed after you re-registered. The only change should have been the mileage at which your battery was registered such that the system now thinks that your battery is new. A certified BMW i mechanic in an i3 Facebook group wrote that i3 battery registration didn't change the charging behavior unlike on BMW vehicles with alternators so that i3 battery registration wasn't really important. Your observation suggests that this isn't true.

Your DC-DC converter output voltage now similar to that of our 2014, 2019, and 2021 i3's. Others have reported higher DC-DC output voltages which I assumed was due to colder ambient temperatures or maybe a voltage measurement inaccuracy.

 

[wegogo]

That's high for the resting voltage of a fully-charged AGM battery. At 25º C, the resting voltage is ~12.8V.

That's not normal behavior. It should shut off when the HV system shuts down within 30 minutes of shutting off an i3. Exceptions would be if HV battery charging is active, the battery pack and/or cabin is being preconditioned, or the voltage of the 12V battery is below a certain level. However, it would stay on to charge the 12V battery for only 1 hour.

View attachment 1740

I forgot to mention that this chart was recorded when my 12V battery was failing (insufficient capacity or failure to hold a charge).

I was wondering if the graph was a readout from your lithium battery...it looks like that lithium battery has an internal charge controller, so it should keep itself happy even if the i3 tries to give it too much juice. In the first part of the graph, are you saying you plugged in the level 1/2 car charger? So you HV system comes on, DC-DC give 14.4 to batter for a few minutes, then drops to a normal 12v battery charge level of about 13.5 until you unplug? So even on your dying battery, it never tried to just keep giving it 14.6 V?

When trying to figure out how to set the battery capacity and type parameters for my 22 Ah LFP battery in BimmerCode, I noticed that there weren't any lithium types and that the AGM type was available only in certain capacities. I chose "40 Ah" to reflect the greater capacity of my LFP battery. I've never noticed any change in the charging behavior when I've made a change to the battery capacity and type, but they I haven't done this much or paid close attention.

I don't recall that 20 Ah AGM wasn't a choice. It's probably unlikely that any BMW would have a tiny 20 Ah flooded-cell lead-acid battery, so I assume that "20 Ah" must be the AGM type.

I assume that BimmerLink displayed your battery as a 20 Ah AGM battery before you re-registered it as the same capacity and type so that your battery hadn't been registered incorrectly in the past which might have explained the DC-DC converter behavior. It's very interesting that the charging behavior changed after you re-registered. The only change should have been the mileage at which your battery was registered such that the system now thinks that your battery is new. A certified BMW i mechanic in an i3 Facebook group wrote that i3 battery registration didn't change the charging behavior unlike on BMW vehicles with alternators so that i3 battery registration wasn't really important. Your observation suggests that this isn't true.

Bimmerlink displaed it as '20 Ah', without the agm. There was no option for 20 Ah AGM in bimmercode, so i re-registered as 20 Ah, keeping it the same in bimmerlink. As a test, I have now coded and re-registered it as '40 Ah AGM'.

Your DC-DC converter output voltage now similar to that of our 2014, 2019, and 2021 i3's. Others have reported higher DC-DC output voltages which I assumed was due to colder ambient temperatures or maybe a voltage measurement inaccuracy.

So far all my measurements are from a decent quality multimeter at the battery terminal, so I trust them. It is 50 F here today.

 

[wegogo]

no luck with coding different battery type - with car plugged in, HV is sill giving 14.5V to the battery, seemingly indefinitely even though it reads as fully charged and gets hot. Obviously I have to assume this battery is dead. So I will report the behavior again once a new battery is installed.

 

[wegogo]

Your DC-DC converter output voltage now similar to that of our 2014, 2019, and 2021 i3's. Others have reported higher DC-DC output voltages which I assumed was due to colder ambient temperatures or maybe a voltage measurement inaccuracy.

The most important difference is that, if I understand you correctly, your DC-DC only sits at 14.5V for a little while (maximum 1 hour when charging a low battery). Your system then lowers the voltage if plugged in or running to around 13-14 V to apply a slower charge or shuts off allowing battery power only to the 12V systems. Mine has so far continued to charge at 14.5+V while car is plugged in for hours. It does not decrease the charge voltage that I can see. And DC-DC only turns off when unplugged.

Thank you for all your data points/experience.

 

[alohart]

I was wondering if the graph was a readout from your lithium battery...it looks like that lithium battery has an internal charge controller, so it should keep itself happy even if the i3 tries to give it too much juice. In the first part of the graph, are you saying you plugged in the level 1/2 car charger?

No, it's the failing original AGM battery in our former 2019 i3. An "Excessive discharge while parked" message had been displayed, so I disconnected the HV disconnect and attached a 12V battery charger on the day before the start of this chart. The 12V battery charger switched from constant current, 0.8A @ 14.2V, to constant voltage, 13.5V, mode at 00:30 on 23 November. Just before 07:00, I disconnected the battery charger when the charger claimed that the battery was fully-charged and connected the HV disconnect. The DC-DC converter turned on at 14.2V. The HV system and thus DC-DC converter turned off automatically a few minutes later with the 12V battery's voltage being only 12.5V despite having just been fully charged by the 12V battery charger. I knew then that the battery was failing and not just discharged, but I didn't have time to install my LFP battery until the following day.

Despite taking 4 short trips with the DC-DC converter on at 14.2V, the 12V battery's voltage continued to decrease. By 18:00, its voltage had decreased to 12.0V at which point the EDME ordered the HV system and DC-DC converter to turn on to charge the 12V battery for 1 hour at 14.2V. By 21:00, the 12V battery's voltage had again decreased to 12.0V again triggering automatic 12V battery charging for 1 hour. By about 22:45, another 1-hour automatic charging session began. The final automatic charging session finished at 01:15 the following day. The EDME must have given up trying to keep the 12V battery charged. By 11:15 the following day when I prepared to replace the battery, its voltage was 11.73V.

So you HV system comes on, DC-DC give 14.4 to batter for a few minutes, then drops to a normal 12v battery charge level of about 13.5 until you unplug?

No, that was my 12V battery charger switching from constant current to constant voltage mode.

So even on your dying battery, it never tried to just keep giving it 14.6 V?

Correct. Until the battery's output voltage decreased to 12.0V, the DC-DC converter behaved normally turning on only when driving and remaining on for a few minutes after shutting off our i3.

 

[alohart]

no luck with coding different battery type - with car plugged in, HV is sill giving 14.5V to the battery, seemingly indefinitely even though it reads as fully charged and gets hot. Obviously I have to assume this battery is dead. So I will report the behavior again once a new battery is installed.

Oh, yeah, your battery is definitely dead. Once the pressure-relief valve on at least one of the battery cells opens, the battery is toast because at least one cell is overheating maybe due to an internal short circuit which would prevent the cell from operating correctly again. Some of its sulfuric acid electrolyte has reacted to form hydrogen sulfide gas (rotten egg odor) and probably hydrogen gas (odorless).

 

[alohart]

The most important difference is that, if I understand you correctly, your DC-DC only sits at 14.5V for a little while (maximum 1 hour when charging a low battery).

My 12V system logger has never measured the DC-DC output voltage as high as 14.5V. Neither has a voltmeter applied between the battery's terminals. In the chart that I posted, the DC-DC converter output was 14.2V when the car was running and when it was automatically charging a discharged 12V battery.

Your system then lowers the voltage if plugged in or running to around 13-14 V to apply a slower charge or shuts off allowing battery power only to the 12V systems.

I've never noticed the DC-DC converter's output voltage varying in a way that I could explain. I have seen it as low as 13.9V, but it normally fluctuates between 14.1V and 14.3V. Maybe the voltage is changing for a reason like the 12V system current is changing as the power demand of 12V components changes. I just don't know.

Mine has so far continued to charge at 14.5+V while car is plugged in for hours. It does not decrease the charge voltage that I can see. And DC-DC only turns off when unplugged.

No EVSE was plugged in when the chart I posted was recording. When HV battery charging is active, the HV system is on and the EDME would order the DC-DC converter to turn on if the 12V battery needed charging (i.e., the EDME's coulomb counting suggested that the 12V battery needed charging). However, current flowing internally due to a 12V battery internal short circuit would not be measured by the IBS, so the EDME's calculation of the 12V battery's charge level would be incorrect. Seems like this would result in the charge level calculation being higher than it actually is, so it would be less likely that the DC-DC converter would be turned on to charge the 12V battery. This isn't what you're experiencing, so I don't have a rational explanation.