12 volt battery in later i3s--watch out

[rougeetnoir]

Here is a story which might be helpful to some later model i3 owners. I have an i3S 2019, 16k, made Feb of 2019, so just 3 years and two months old. Most of the stories about the 12 volt battery seem to involve earlier cars, 2014-16 &c. Anyhow, I came out to my car in a tight garage the other morning after having put it away on charge and it was a brick, no response to key fob, no lights, horns &c. I thought it likely to be the 12 v battery and having got it towed the dealer, that was what it was. But instead of giving warning signs, quirky lights, windows, &c. it just went completely dead.

So a new battery and I am back on the road, but typically these problems have occurred in 4-5 year old batteries, so owners in the three year range might want to consider getting one of the batteries and keeping it on trickle charge. Or just change it at 3 years as a matter of prevention.

Fortunately my car was under extended warrantee and the dealer had a battery so I was OK for the towing and the work.

 

[eNate]

There years falls within the range of "typical life expectancy." That doesn't seem unusual based on the posts I've read.

 

[agzand]

There are some factors that affect battery life, for example cold weather, not driving long distances frequently.

 

[alohart]

There are some factors that affect battery life, for example cold weather, not driving long distances frequently.

No cold weather here, but our 2014 i3 has never driven more than 100 miles round-trip (impossible … an isolated island). With less than 13k miles driven since new, the average charge level of our 12 V battery was so low that I had to charge it with a battery charger several times to prevent it from discharging so much that drive readiness state could not be entered. Remaining at a low charge level for extended periods isn't great for a lead-acid battery, yet it lasted more than 8 years before it wouldn't hold a full charge. Battery life seems pretty unpredictable.

 

[Gen]

Here is a story which might be helpful to some later model i3 owners. I have an i3S 2019, 16k, made Feb of 2019, so just 3 years and two months old. Most of the stories about the 12 volt battery seem to involve earlier cars, 2014-16 &c. Anyhow, I came out to my car in a tight garage the other morning after having put it away on charge and it was a brick, no response to key fob, no lights, horns &c. I thought it likely to be the 12 v battery and having got it towed the dealer, that was what it was. But instead of giving warning signs, quirky lights, windows, &c. it just went completely dead.

So a new battery and I am back on the road, but typically these problems have occurred in 4-5 year old batteries, so owners in the three year range might want to consider getting one of the batteries and keeping it on trickle charge. Or just change it at 3 years as a matter of prevention.

Fortunately my car was under extended warrantee and the dealer had a battery so I was OK for the towing and the work.

My i3Rex was bought in 2018 and I’ve done 66,000 miles. I wondered about the 12 V battery and asked them whether I should replace it and they said because I do such a good mileage that it wouldn’t be necessary. Not sure whether I really understand that answer, maybe you can enlighten me

 

[mojo]

The reason is that if the car is sitting idle, there are few things that will cause the car's DC-DC converter to power on, so the 12V battery seldom gets charged. If, however, the car is used frequently, the 12V battery gets charged frequently (all the time the car is being driven, and all the time the car is being charged) and so is less likely to deteriorate.

 

[Gen]

The reason is that if the car is sitting idle, there are few things that will cause the car's DC-DC converter to power on, so the 12V battery seldom gets charged. If, however, the car is used frequently, the 12V battery gets charged frequently (all the time the car is being driven, and all the time the car is being charged) and so is less likely to deteriorate.

Thank you for taking the trouble to reply so promptly- I am 87 and living alone so don’t want any nasty surprises!

 

[mojo]

don’t want any nasty surprises!

That's understandable. One approach is just to keep an eye on it, or another is just pre-emptive maintenance and have the garage replace it in a year or two's time.

There's nothing special about the 12V battery, so there's every reason to expect that it will have a working life of maybe six years, give or take a few. I'm expecting to change mine at 6 years old, whether it's showing any signs of deterioration or not! If you're in the UK they are not very expensive, but a fair bit more costly in the US, it seems.

 

[Simoni3]

or fit a bluetooth battery monitor on the 12V and you;ll be able to see the V over time
mine, after 77k miles is just starting to drop a bit when 'starting', new battery about to be fitted

 

[McDuff]

There are some factors that affect battery life, for example cold weather, not driving long distances frequently.

I don't understand how your driving habits will affect the charge of the 12v battery: it's charged from the traction battery, not by an alternator while driving. Is there something in the system that reduces the tendency of the HV battery to keep the 12v battery charged?

 

[McDuff]

Here is a story which might be helpful to some later model i3 owners. I have an i3S 2019, 16k, made Feb of 2019, so just 3 years and two months old. Most of the stories about the 12 volt battery seem to involve earlier cars, 2014-16 &c. Anyhow, I came out to my car in a tight garage the other morning after having put it away on charge and it was a brick, no response to key fob, no lights, horns &c. I thought it likely to be the 12 v battery and having got it towed the dealer, that was what it was. But instead of giving warning signs, quirky lights, windows, &c. it just went completely dead.

So a new battery and I am back on the road, but typically these problems have occurred in 4-5 year old batteries, so owners in the three year range might want to consider getting one of the batteries and keeping it on trickle charge. Or just change it at 3 years as a matter of prevention.

Fortunately my car was under extended warrantee and the dealer had a battery so I was OK for the towing and the work.

I haven't found a way to charge the 12v battery with a charger; my X3 has terminals under the bonnet with which I can charge the 12v battery, which is in the boot).

 

[alohart]

I haven't found a way to charge the 12v battery with a charger; my X3 has terminals under the bonnet with which I can charge the 12v battery, which is in the boot).

An i3 has 12 V terminals under the rear cargo floor access panel that could be used to charge the 12 V battery. However, it's easier to connect a charger directly to the battery terminals in the frunk. Connecting the negative cable is pretty easy while connecting the positive cable is more difficult because of the red plastic cover over the terminal. The charger cable can be connected to the positive battery clamp tightening bolt which is on the left side of the terminal to the rear of the plastic cover. This can be done without removing the frunk box, but it's easier with the frunk box removed.

In any event, be sure to disconnect the high-voltage disconnect underneath the cover to the right of the frunk box. This prevents the DC-DC converter from potentially turning on to charge the 12 V battery while the battery charger is connected. If the battery charger's voltage is higher than the DC-DC converter's output voltage, current might flow backward into the DC-DC converter which might not be a good thing. The DC-DC converter is part of i3's most expensive electronic module, the electric motor electronics (EME), so I would not risk damaging it.

 

[rougeetnoir]

I have just bought a new 12 v. battery as insurance against the one I replaced about 1 1/2 year ago failing. So I want to keep it in the garage on a trickle charger to insure that it does not deteriorate. Any advice on doing this? Thanks in advance

 

[Marty]

i added a second battery in parallel to original battery,with a 40 amp fuse inbetween, i did it because my wife would go shopping for awhile and i wanted to stay warm or cool depending on temp. With single battery,with ac or heat on,the single battery would run down, also you can check battery health with an inexpensive voltmeter that plugs in the cig. Liter plug under center dash( amazon).

 

[McDuff]

An i3 has 12 V terminals under the rear cargo floor access panel that could be used to charge the 12 V battery. However, it's easier to connect a charger directly to the battery terminals in the frunk. Connecting the negative cable is pretty easy while connecting the positive cable is more difficult because of the red plastic cover over the terminal. The charger cable can be connected to the positive battery clamp tightening bolt which is on the left side of the terminal to the rear of the plastic cover. This can be done without removing the frunk box, but it's easier with the frunk box removed.

In any event, be sure to disconnect the high-voltage disconnect underneath the cover to the right of the frunk box. This prevents the DC-DC converter from potentially turning on to charge the 12 V battery while the battery charger is connected. If the battery charger's voltage is higher than the DC-DC converter's output voltage, current might flow backward into the DC-DC converter which might not be a good thing. The DC-DC converter is part of i3's most expensive electronic module, the electric motor electronics (EME), so I would not risk damaging it.

Thank you. I'll leave well alone

 

[eNate]

i added a second battery in parallel to original battery,with a 40 amp fuse inbetween, i did it because my wife would go shopping for awhile and i wanted to stay warm or cool depending on temp. With single battery,with ac or heat on,the single battery would run down, also you can check battery health with an inexpensive voltmeter that plugs in the cig. Liter plug under center dash( amazon).

If the AC or heat is running, that power is coming from the high voltage battery. The small 12 volt battery may run just the blower motor – unsure there – but in general it's used for running the computer and telematics modules, accessory lights, and closing the contactors to engage the traction battery.

 

[JimBmwi3s]

Marty, Is there a YouTube video or instructions somewhere showing how to add a 2nd battery

 

[alohart]

I have just bought a new 12 v. battery as insurance against the one I replaced about 1 1/2 year ago failing. So I want to keep it in the garage on a trickle charger to insure that it does not deteriorate. Any advice on doing this?

I've done this since 2017 when several 2014 i3 owners began reporting 12 V battery failure. I ordered an AUX18L from a local East Penn Manufacturing retailer which was considerably less expensive than buying a battery from our local BMW dealer. East Penn Manufacturing supplies batteries to BMW, Remy, and others who relabel the battery. Because AGM batteries have a lower self-discharge rate than flooded-cell lead acid batteries, charging it frequently isn't necessary, so I charged it fully about twice each year rather than leaving a trickle charger connected at all times. Leaving an AGM battery on a trickle charger fully charged at all times might shorten its life compared with charging it fully periodically. The original battery lasted more than 7 years, and I sold our 2014 i3 only 6 months after replacing its 12 V battery, so I don't know whether it's still working.

I bought a used 2019 i3 in 2022. Another local i3 owner with a 2019 i3 was concerned about 12 V battery failure, so we bought a replacement battery to store until either of us needed it. In Honolulu, East Penn Manufacturing would supply an AUX18L battery only to the BMW dealer, so we were unable to buy a battery from a local East Penn Manufacturing retailer as I had done previously. Remy and other online retailers don't ship batteries to Honolulu, so we had to buy it from our BMW dealer.

The 12 V battery in our 2019 i3 failed last November, almost 5 years after our i3 was manufactured. In May, 2023, I began testing a lithium iron phosphate (LFP) battery in our i3 for its manufacturer. Rather than replacing the failed original battery with an AUX18L, I replaced it with a LFP battery which has worked well since. I have a second LFP battery as a backup, so I don't need our replacement AUX18L The other 2019 i3 owner sold his i3 when it warranty expired, and the new owner didn't want our replacement battery. We sold it to another local i3 owner, so I don't know whether storing it shortened its life.

I recommend installing a 12 V system monitor to help detect when the 12 V battery is failing before it fails.

 

[alohart]

If the AC or heat is running, that power is coming from the high voltage battery. The small 12 volt battery may run just the blower motor – unsure there – but in general it's used for running the computer and telematics modules, accessory lights, and closing the contactors to engage the traction battery.

Plus the 12 V battery would be charged from the high-voltage battery via the DC-DC converter, so it would not discharge when the high-voltage system is on. There are very few situations in which the 12 V battery would be powering 12 V loads without being charged by the DC-DC converter, so adding a second 12 V battery seems really unnecessary.

 

[alohart]

i added a second battery in parallel to original battery,with a 40 amp fuse inbetween, i did it because my wife would go shopping for awhile and i wanted to stay warm or cool depending on temp. With single battery,with ac or heat on,the single battery would run down, also you can check battery health with an inexpensive voltmeter that plugs in the cig. Liter plug under center dash( amazon).

This doesn't make sense to me. When the climate control system is on, the high-voltage (HV) system is on because the A/C compressor and cabin resistance heater are HV devices. The 12 V battery management system in the electric digital motor electronics (EDME) would turn on the DC-DC converter to charge the 12 V battery when it senses either low 12 V battery voltage or high 12 V current flowing out of the battery. This is easy to determine by measuring the 12 V system voltage with your voltmeter. If the voltage is <13.0 V, the 12 V battery isn't being charged and is powering all 12 V loads itself which would discharge it. If the voltage is >14.0 V, the DC-DC converter is providing power to the 12 V system which would be used to power 12 V loads and charge the 12 V battery.

By installing a second battery, you effectively increased the capacity of the 12 V battery from the EDME's perspective. If you didn't tell the body domain controller (BDC) that the 12 V battery's capacity increased (e.g., using BimmerCode to change the Battery Type to that with a higher capacity), the EDME might not be able to manage your 2 batteries ideally which could reduce their lives.

If your 12 V battery is discharging when your i3 is parked with the climate control system on, the battery, the intelligent battery sensor (IBS), the EDME, or the DC-DC converter must be failing. Even with all 12 V loads on, their total power consumption would almost certainly be less than the maximum DC-DC converter output power of 2.5 kW, so the 12 V battery should not discharge if everything is working correctly.

It's almost impossible to check the 12 V battery health with a voltmeter plugged into an auxiliary power port. I had hoped that this would work when I installed a voltmeter in the auxiliary power port below the center of the dashboard in 2016. It quickly became apparent that the voltage being displayed was almost always the output voltage of the DC-DC converter, not the 12 V battery. The HV system turns on when the doors, hatch, or frunk are unlocked/locked or opened/closed, when battery pack charging or preconditioning is active, when an i3 is in the drive ready state, or for 1 hour when the EDME determines that the 12 V battery needs charging while an i3 is parked with the HV system off. The HV system remains on for up to 30 minutes after the occurrence of the last event that caused it to turn on.