Rotten Eggs smells and a hot 12-volt battery

[smytherrrs]

I saw another post about a “sulfur smell” and hot twelve volt battery, which the owner replaced, so I am curious how common issues are with the 12v battery…

On my drive home today with the windows down, I noticed a distinctive smell of rotten eggs. The natural gas-powered city bus next to me was surely to blame, but it did not dissipate as I got closer to home.

I pulled in the garage, closed the garage door, and almost puked at how pungent the smell was. I got under the car and noticed some steam behind the passenger-side front wheel and small drips of clear liquid every couple of seconds from a tube that appears to be a vent tube for the 12v battery. Fearing the smell or a potential fire would ruin my garage, I moved it outside and went back inside.

After 20 minutes, I heard a distinctive BMW car alarm going off. I walked out and found the car battery mostly dead but the siren blaring and lights on, albeit fairly dim. The key fob didn’t work to unlock the car or silence the alarm. I used the physical key to open the door. The electric hood release didn’t work, so I had to pull the plastic door off below it and pull the cable to manually release the hood. I disconnected the high voltage battery with the sort of fuse box at the front of the hood but didn’t touch the 12v since it is a Saturday night and BMW Roadside Assistance didn’t have any “master technicians” available to confirm it was safe to do so. The car alarm went off after an hour or so, despite the 12v battery appearing to have some juice left, evidenced by the flashing red light under the rear view mirror.

I am anxiously awaiting a tow and very happy I have a month left on my Roadside Assistance package. I am speculating that i3’s have a fairly primitive system to charge the 12v with the high voltage battery and mine is the original 12v from 2016. I speculate the 12v needs to be replaced every 3 years or so to ensure the battery doesn’t degrade as mine apparently has. I will report back with the service center findings!

 

[Arm]

I don't understand how they can design a car that relies so heavily on a stupid 12v auxiliary battery in such a negative way. It boggles my mind what the engineers were thinking.

 

[frictioncircle]

Hello smytherrs –

Wow, I've not seen anyone post about this failure before!

What year is your i3 and is the 12V battery original to the car? They usually last about five years.

 

[smytherrrs]

I don't understand how they can design a car that relies so heavily in a stupid 12v auxiliary battery in such a negative way.

It seems ludicrous that I should need to use my physical key to access the car when the high voltage battery has at least 60% charge.

What year is your i3 and is the 12V battery original to the car? They usually last about five years.

It is a 2017 i3 REx, which I bought used with ~20k miles in December 2019. I haven’t had the 12v replaced, so I am 90% certain it is the original battery, which is coming up on 5 years of age.

A picture of the vent tube that was dripping/steaming:

 

[keepgoing]

My BEV is 2014 with in service date Dec 2014. The original 12v battery last till this June. I changed it on June 2021 with Odometer at 61K miles. There is a vent hose that I needed to disconnect and reconnect during the replacement, but I did not trace the vent hose connection to see where it leads to. The issue that prompted me to change the battery was the Comfort Access no longer works by touching the door handle to lock or unlock, but using the key fob's button is fine. Then within two days, the car displayed Excessive discharge upon startup, but I was still able to drive it multiple days without getting disabled or anything. I decided to change it before it got worse. The old battery measured at 11.70v upon removal from the car, there is definitely no swelling or other physical deformation seen from the outside. I bought the replacement battery from remybattery.

 

[smytherrrs]

Then within two days, the car displayed Excessive discharge upon startup, but I was still able to drive it multiple days without getting disabled or anything. I decided to change it before it got worse.

Smart! I had the excessive discharge warning, but it wasn’t the severe type of warning that would have led me to believe I needed to stop driving and seek service immediately. I drove it for a week or two before this happened. Excessive discharge warnings should probably be serviced with some immediacy.

 

[alohart]

Excessive discharge warnings should probably be serviced with some immediacy.

True, but the service might be merely charging a discharged 12 V battery rather than replacing it. The excessive discharge warning occurs due to a low 12 V system voltage which could be due to a good 12 V battery not being charged sufficiently. This happened with our 2014 i3 with its original battery last January. Due to the pandemic, our i3 had been driven much less than previously allowing 12 V vampire loads to gradually discharge its 12 V battery. After fully charging the battery with a battery charger, this warning hasn't been displayed since, and the 12 V battery has been been behaving normally.

So rushing to replace a 12 V battery when an excessive discharge warning is displayed might be unnecessary and wasteful.

 

[botzata]

Hello everyone!

I wanted to share our story about the failed 12v battery since it was scary. We have a 2018 i3. A few weeks ago, we also noticed the "rotten egg" smell in our garage. We didn't know where the smell is coming from at the time (there was no check control messages in our bmw related to the battery). After a couple of days, the smell got so strong, and it started leaking inside the house--you could barely stay inside the house. We thought that we had a gas leak and called the gas company. In turn, they called the fire department. After 20-30 mins of investigating the situation, it turned out that it was the 12v battery of our i3. Apparently, when the battery gets old and needs to be replaced, if you try to recharge the battery, it starts boiling and produces hydrogen sulfide gas, which is extremely flammable and poisonous. The levels in our house were 4x higher than normal. We had to evacuate our family in the middle of the night, and the fire department had to blow out the house with giant fans for an hour to get the toxic gas out. We were told that such levels of hydrogen sulfide are not only unhealthy but can also easily lead to a fire. We were lucky that we were still awake that night, and we acted fast.

The problem is that the car didn't give us any check control messages that there is an issue with the battery (acid leaking). We simply had no idea, so hopefully, if you experience something similar, you should know that it's likely the 12v battery leaking acid (when you try to charge the car). Rather, everything happened rather suddenly and could have had catastrophic consequences. In my mind, this is a serious safety issue. I think there were two opportunities to prevent this catastrophic failure. First, the car should give you a warning that the battery is leaking and needs to be replaced. Second, the issue occurs only when the 12v battery is being charged, so the car could have a safety fail and stop charging the battery if a leak happens.

We called BMW of North America. At first, they were very apologetic for the situation, promised that they will cover all the cost of the battery replacement, look into the issue, etc. The battery was replaced at a local dealership. BMW then asked us to sign a non-disclosure agreement and never talk about the accident with anyone if we want them to cover the charges (close to $900). I felt uncomfortable doing this since I believe that the issue is not just the battery but the failed safety system of the car that can potentially endanger the life of others. I asked them if the car has any fail safety measures to prevent a catastrophic failure of the battery like this one in the future. The people at the dealership were quite incompetent and didn't have an answer. But the BWM representative suddenly started lying and changed his story once I said that I will not sign the non-disclosure agreement. He said that we received a check control message, so it was our responsibility to take care of the battery. I took a video before the car was towed, and the diagnostic that was run on the car by the BMW dealership clearly shows that there were no check control messages related to the battery (only low tire pressure).

In any case, this has been a very frustrating experience for us and I wanted to share it here in case you experience something similar.

 

[alohart]

Apparently, when the battery gets old and needs to be replaced, if you try to recharge the battery, it starts boiling and produces hydrogen sulfide gas, which is extremely flammable and poisonous.

There's no liquid sulfuric acid in an i3's standard AGM battery, so there's nothing to boil. The sulfuric acid is absorbed in glass fiber mats which allows an AGM battery to be mounted in any orientation, even upside-down, because there's no liquid electrolyte to leak out. However, if the sulfuric acid is above 60º C which is below its boiling point, hydrogen sulfide gas (H2S) could be produced when a battery is being charged.

A bit of a mystery to me is why the battery would be charging while an i3 is parked. Maybe the battery's voltage dropped below 12.0 V when the DC-DC converter could automatically turn on to charge the battery. Also, why would the battery be above 60º C? Maybe a partial internal short circuit, high internal electrical resistance, an abnormal electrochemical or chemical reaction, or something else could raise the temperature above 60º C. In any event, the battery has failed and is dangerous, so it needs to be disconnected and replaced ASAP.

An AGM battery is sealed, but each cell has a pressure relief valve that would open if enough H2S, H2, or SO2 is produced. With the original AUX18L battery, all cells vent to a common vent tube to which is attached a hose exiting under an i3. Those who replace the original battery with an ETX18L power sports battery won't have this vent hose directing the H2S, H2, SO2, and other gasses out of the frunk which could allow them to accumulate. An ignition source in the frunk could then ignite the flammable gasses which could result in an explosion. Fortunately, an ignition source in the frunk is probably fairly unlikely.

The levels in our house were 4x higher than normal. We had to evacuate our family in the middle of the night, and the fire department had to blow out the house with giant fans for an hour to get the toxic gas out. We were told that such levels of hydrogen sulfide are not only unhealthy but can also easily lead to a fire. We were lucky that we were still awake that night, and we acted fast.

Yikes! Thankfully, nothing worse happened.

The problem is that the car didn't give us any check control messages that there is an issue with the battery (acid leaking). We simply had no idea, so hopefully, if you experience something similar, you should know that it's likely the 12v battery leaking acid (when you try to charge the car).

No leaking could occur unless the battery had been replaced previously by a flooded-cell battery which is unlikely. There's no temperature sensor on the battery that could have warned you about an overheating battery. About the only warning that could be displayed is when the battery's voltage decreases below a certain level or maybe decreases too rapidly. I and many others have seen such a warning message which could indicate a failing battery or a battery that just needs charging.

Rather, everything happened rather suddenly and could have had catastrophic consequences. In my mind, this is a serious safety issue.

Fortunately, the battery failure mode that you experienced seems to be pretty unusual, but certainly not unheard of, and could happen in any vehicle with a lead-acid battery. I'm not aware of any vehicle having sensors that could have warned you about the problem before it became dangerous.

 

[frictioncircle]

Hello botzata and welcome to the forum!

Thank you very much for signing up here to post such a thorough account of your 12V battery issue. I've been here a while and yours is only the second time I've seen this issue (thanks alohart for directing everyone to this thread).

I would be completely freaked out had something similar happened to me.

In particular I'm very disappointed in BMW NA putting an NDA under your nose before they'd cover your expenses. Granted, you're probably outside of warranty and whatever they covered under "goodwill" (honestly, I've found their post-warranty goodwill to be very helpful over the many years I've been a customer) wasn't too much out of their pocket, but the fact that the BMW rep lied to you when you declined to sign? That's dirty business.

I wouldn't doubt that NHTSA or a pro-consumer organization (Consumer Watchdog, etc.) would find your story interesting.

 

[weajd]

I don't understand how they can design a car that relies so heavily on a stupid 12v auxiliary battery in such a negative way. It boggles my mind what the engineers were thinking.

Well the high voltage battery is over 200 volts and the semiconductors in the car like a voltage of 12 volts or less. While the high voltage battery is turned off, the circuits in the car rely on the 12 volt battery to keep their state and to provide the accessories you like.
The better question is why they made it so small and difficult to replace. The rectangular bucket in the the frunk is a better place to put a larger 12 volt battery.

 

[alohart]

I don't understand how they can design a car that relies so heavily on a stupid 12v auxiliary battery in such a negative way. It boggles my mind what the engineers were thinking.

All EV's have a 12 V battery that performs the same functions as that in an i3. The engineers were thinking that eliminating the 12 V battery and powering everything with the Li-ion battery pack whose voltage can be as high as 400 V could be deadly. Keeping a DC-DC converter running continuously to reduce the high voltage to ~14 V to power the many 12 V loads would discharge the battery pack faster than most people would accept. No engineer has a design that could safely eliminate a 12 V battery in an EV and that would be acceptably efficient.

The 12 V battery in every ICE vehicle could fail in the same ways as that in an i3, yet a 12 V battery has been used for over a century because the probability of a really dangerous failure is quite low.

 

[alohart]

The better question is why they made it so small and difficult to replace. The rectangular bucket in the the frunk is a better place to put a larger 12 volt battery.

Because the DC-DC converter turns on to provide up to 2.5 kW of 12 V power whenever the 12 V battery's voltage drops below a certain limit, the 12 V battery doesn't need to have a large capacity unlike an ICE vehicle whose 12 V battery must be powerful enough to power a starter motor in very cold conditions and to provide power when its engine isn't running. A large, heavy battery would be a waste in a car designed to be as light as possible.

 

[wegogo]

Add me to the list of people who have experienced this issue. Extremely frightening - after parking the i3 and plugging in my charger, I leave in my 750lix. I come home and open the garage (which I now know could have exploded if I hadn't come home - gas water heater in garage), and it reaks of burning plastic/oil/sulfur. I think the 750 must be burning some oil today - nope, the smell is getting stronger. I move the cars in and out, isolating the smell to the i3. The i3 sits outside for hours while I research. After finding this and other threads, I pop the frunk and feel the 12V battery. It is still hot enough to burn someone after the car being unplugged and powered off. And the sulfur smell is still pouring out of the battery.

The car has yet to produce any warnings about anything. And certainly no warnings about the 12v battery. It would be interesting to check codes/voltages to see what the behavior is. From what I can tell, if it is unplugged and off, it will not charge the 12v battery. But plugged in or running, it must be pumping A LOT of current into that battery. Any intelligent DC-DC design would have something like the Texas Instruments BQ24450 integrated to the charge system to monitor temperature, charge, and failure states of the 12 battery. And as a failsafe, you would monitor the time a certain amperage is being applied to a 12v battery. I.e., if(charge amps > 10 and < 20, shutoff after 3 hours so you dont burn down the house and kill people).

Essentially, BMW must have just decided to dump energy in without regulation from a battery charging controller ($2 IC + engineering or $100 ready made product). This is kind of how it works on ICE cars, like someone mentioned above, EXCEPT in ICE cars, you are only dumping unregulated energy into the battery while the car is running, usually at speed, as the alternator current output is very low at idle. This means the runaway charge situation occuring here (in a closed garage) could only happen if you left your ICE car running with a brick on the throttle in your closed garage - a very unlikely scenario. Charging your EV in a closed garage, however, is a very LIKELY scenario.

Now, do I think they are idiots for the engineering oversight? Not really...all cars have stupid problems. The i3 is a fantastic piece of engineering, mechanical and electrical. It is complex, and it was a new venture. What is frightening about this is that there is not a recall for it...All of these i3's are eventually going to be owned by people who do not take their car into BMW for maintenance. And if the batteries can fail like this, people must be having fires occur...but I guess if they can cover up most cases with an NDA, or charge so much to fix anything most people have to dump the cars........ah the strategies of admin/business scum.

 

[mojo]

The car has yet to produce any warnings about anything. And certainly no warnings about the 12v battery.

There's some evidence to suggest that BMW may have changed this behaviour in later cars. There is definitely evidence that some models monitor the 12V battery voltage and can switch on the DC-DC charger even when the car is not itself powered up. And on my car (2021) there is definitely a voltage monitoring function that generates a warning message with wording that approximates to "Excessive battery discharge while parked". I don't know exactly how the monitoring works, but I have seen the message after leaving the car parked for a long time. It's also not a well thought-out message, because the wording is ambiguous - it's not clear whether it refers to the 12V battery or the HV battery.

I suspect that the practical difficulty in monitoring how much current is going into the battery is that there is no easy way for the car to distinguish between what is going into the battery and what is going into - for example - the sound/infotainment system, and other electrical consumers on the car.

 

[wegogo]

There's some evidence to suggest that BMW may have changed this behaviour in later cars. There is definitely evidence that some models monitor the 12V battery voltage and can switch on the DC-DC charger even when the car is not itself powered up. And on my car (2021) there is definitely a voltage monitoring function that generates a warning message with wording that approximates to "Excessive battery discharge while parked". I don't know exactly how the monitoring works, but I have seen the message after leaving the car parked for a long time. It's also not a well thought-out message, because the wording is ambiguous - it's not clear whether it refers to the 12V battery or the HV battery.

I suspect that the practical difficulty in monitoring how much current is going into the battery is that there is no easy way for the car to distinguish between what is going into the battery and what is going into - for example - the sound/infotainment system, and other electrical consumers on the car.

Current sensors are often attached or close to the battery terminal on 12v systems. My 2013 acadia has it, and will use it to warn if there is a charging issue. It really is trivial, there just seems to be an oversight in the initial models of the i3 - or maybe they have it, but there is simply a programming defect that doesn't cover the situation where a 12v battery is low but won't take a charge.

 

[808Pants]

Essentially, BMW must have just decided to dump energy in without regulation from a battery charging controller ($2 IC + engineering or $100 ready made product). This is kind of how it works on ICE cars, like someone mentioned above, EXCEPT in ICE cars, you are only dumping unregulated energy into the battery while the car is running, usually at speed, as the alternator current output is very low at idle. This means the runaway charge situation occuring here (in a closed garage) could only happen if you left your ICE car running with a brick on the throttle in your closed garage - a very unlikely scenario. Charging your EV in a closed garage, however, is a very LIKELY scenario.

Wha...? Back up a little. I'm unaware of any ICE vehicle ever designed without voltage regulation, whether from generator or alternator, and certainly this isn't the case with the i3. This is fundamental. Are they immune to failure? Well, what is?... but I haven't read about anything like you experienced, either, so maybe it's just bad luck and a very isolated incident.

Any regular reader of this forum has come across 12V battery-failure concerns. I installed a BM-6 Bluetooth monitor (for multiple vehicles, vs. the BM-2) so I could, with luck, get an early warning of impending failure. As is displayed on the smartphone monitoring your 12V battery, the 12V charging cycle plot is 'sawtooth'. As the battery approaches failure, the teeth become closer together. Here's one post that illustrates.

I can't recommend the BM-6 because it's never clear when I'm connected to which battery, and it's unnerving in always telling me that Bluetooth isn't on regardless - which makes the basic concept of getting an alert when voltage drops to, say, 12.2V seem pretty unreliable. I think (but not sure) that the BM-2 permits a user to set an alert that's based simply on that voltage, and not a percentage of capacity or whatever else the designers thought would appeal to users - who are mostly going to be ICE-vehicle drivers.

 

[eNate]

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

 

[alohart]

From what I can tell, if it is unplugged and off, it will not charge the 12v battery.

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.

But plugged in or running, it must be pumping A LOT of current into that battery. Any intelligent DC-DC design would have something like the Texas Instruments BQ24450 integrated to the charge system to monitor temperature, charge, and failure states of the 12 battery. And as a failsafe, you would monitor the time a certain amperage is being applied to a 12v battery. I.e., if(charge amps > 10 and < 20, shutoff after 3 hours so you dont burn down the house and kill people).

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.

Essentially, BMW must have just decided to dump energy in without regulation from a battery charging controller ($2 IC + engineering or $100 ready made product).

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.

What is frightening about this is that there is not a recall for it...All of these i3's are eventually going to be owned by people who do not take their car into BMW for maintenance. And if the batteries can fail like this, people must be having fires occur...but I guess if they can cover up most cases with an NDA, or charge so much to fix anything most people have to dump the cars........ah the strategies of admin/business scum.

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.

 

[wegogo]

Wha...? Back up a little. I'm unaware of any ICE vehicle ever designed without voltage regulation, whether from generator or alternator, and certainly this isn't the case with the i3. This is fundamental. Are they immune to failure? Well, what is?... but I haven't read about anything like you experienced, either, so maybe it's just bad luck and a very isolated incident.

Any regular reader of this forum has come across 12V battery-failure concerns. I installed a BM-6 Bluetooth monitor (for multiple vehicles, vs. the BM-2) so I could, with luck, get an early warning of impending failure. As is displayed on the smartphone monitoring your 12V battery, the 12V charging cycle plot is 'sawtooth'. As the battery approaches failure, the teeth become closer together. Here's one post that illustrates.

I can't recommend the BM-6 because it's never clear when I'm connected to which battery, and it's unnerving in always telling me that Bluetooth isn't on regardless - which makes the basic concept of getting an alert when voltage drops to, say, 12.2V seem pretty unreliable. I think (but not sure) that the BM-2 permits a user to set an alert that's based simply on that voltage, and not a percentage of capacity or whatever else the designers thought would appeal to users - who are mostly going to be ICE-vehicle drivers.

Yes, alternators have a regulated voltage, they will try to push 14.X Volts to whatever load they are given, making current (mostly)unregulated, as the alternator does not have knowledge of the load. It will give current up to its limitation at its spinning rpm (newer cars have more ECM controlled regulation than this for efficieny). Thus, the energy that can be delivered to a battery per second is unregulated, other than by limitation (which would be way too high - 100A is way to much to shove in a battery except for jump start).

I'm new to the i3 and the forum, but I will definitely look into voltage monitor for this.