Warranty replacement of 12 V battery

[alohart]

If our 12 V battery is failing as I believe it is, BMW of Hawaii wants to replace it with a larger, heavier, flooded-cell battery used in other BMW models rather than the smaller, lighter, absorbent glass mat (AGM) factory battery. RealOEM probably shows the alternatives:

Description                                                    Size         Part #
Original BMW AGM-battery                        20 AH     61219321815
Original BMW battery (Warranty only)     40 AH     61217635788

The 40 Ah battery is used in F30 and F31 BMW's. I want the 12 V battery designed for the i3.

An i3 owner who wanted a larger capacity 12 V battery ordered the 40 Ah battery above but had to modify the battery tray and move the windshield washer fluid reservoir to install the physically larger battery. I would not want that done and would be surprised that BMW would do that just to install a warranty replacement battery that dealers are more likely to stock.

For those who have had their 12 V batteries replaced under warranty, which battery was installed?

 

[TOEd]

At 12,620 km and 5 months our new 2015 i3 12 volt battery was found to be defective during a condition based service oil change. No symptoms. Computer check indicated faulty battery. Replaced with smaller agm battery. No subsequent problems. Currently at 37,000 km (1 year and 8 months).

In a roll over or other serious accident agm battery is far less likely to leak. I would stick to smaller agm battery.

 

[jadnashuanh]

AGM batteries are much better at extreme discharge than flooded cell ones. the i3 would tend to benefit from that. Now, there are probably larger AGM batteries that could be used, and a larger one would be less stress, because in normal circumstances, it wouldn't be discharged as much as the smaller one.

 

[TOEd]

Forgot to mention that during past 40 years I have owned probably 20 agm batteries. They were used in a car, snowmobiles and a motorcycle. They usually lasted a year or two. The agm in my diesel smart lasted 2 and a half years. So I replaced it with a $10 flooded "blem" battery. Best $10 I have ever spent. 10 years and 170,000 km later it is still good (just checked it). Blems, for those unfamiliar with the term, are unlabeled seconds or defective batteries sold for cheap.

So I can appreciate your dealer suggesting a flooded battery. Not a bad option for those wanting long life from their battery.

 

[jadnashuanh]

FWIW, the AGM battery in my GT is now over 4-years old and still working. The battery type utilized will depend somewhat on how the car is designed. An AGM battery tends to last longer when subjected to deeper discharge. In a typical ICE, the battery needs a big surge to start the car, then the alternator provides nearly all of the power. In my GT, they have the alternator on a clutch like an a/c compressor, and it doesn't always run, mostly when you let off on the gas pedal and are slowing. In the interim, it is relying on the battery. I think the i3 uses a similar technique. Also, an AGM battery will tend to use a slightly higher voltage during charging, and that can mess up a standard battery. On my GT, you can program the car to adjust to the type and size of the battery installed...I do not know if that's also true on the i3, but the curve and limits are different when properly optimized for the battery installed. On the GT, it also takes into account the age of the battery to handle expected degradation over time.

It's not always simple...today's cars are quite a bit more complex than they were even a few years ago.

 

[alohart]

Forgot to mention that during past 40 years I have owned probably 20 agm batteries. They were used in a car, snowmobiles and a motorcycle. They usually lasted a year or two.

Maybe your AGM batteries were low quality or were being charged at too high a voltage. The charging voltage of an AGM battery is lower than that of a flooded-cell battery.

The Odyssey AGM battery in the 2000 Honda Insight that we sold in July was 7 years old, so under the right conditions, an AGM battery can have a long life. Our Insight's original flooded-cell battery failed after 3 years, possibly because the Insight's rather low-voltage 12 V charging system was better suited to an AGM battery.

Maybe the i3's AGM battery is low quality as well. If after the battery warranty expires and if the life of BMW's replacement AGM battery is no better than 3 years, I'll install a high-quality Odyssey AGM battery.

So I can appreciate your dealer suggesting a flooded battery. Not a bad option for those wanting long life from their battery.

The i3's 12 V charging system is set to charge an AGM battery, not a flooded-cell battery, so a flooded-cell battery might not last as long as it should.

 

[gt1]

In my opinion, a regular charging battery is not appropriate for i3, which has no conventional charger. A deep cycle (marine) type should be better.

 

[alohart]

In my opinion, a regular charging battery is not appropriate for i3, which has no conventional charger. A deep cycle (marine) type should be better.

I have a 12 V voltmeter installed in the power port under the entertainment system/climate controls so I can monitor the 12 V system voltage. The 12 V charging system does not allow the 12 V battery's voltage to drop below ~12.0 V (the low voltage limit is probably a bit higher), so the 12 V battery is never deep-cycled; when the 12 V battery's voltage drops below this low voltage limit, the DC-DC converter turns on to charge the 12 V battery using power from the Li-ion battery pack.

To the 12 V battery, the 12 V charging system looks similar to a conventional voltage-regulated alternator, so a standard 12 V starter battery in an i3 is probably superior to a deep cycle battery.

 

[gt1]

I'm not an expert in the battery chemistry, but usually all features are compromises. The high current capability of the charging battery is probably built at expense of capacity or something else. And i3 doesn't benefit from high current.

 

[TOEd]

:lol: I find info at this website useful:
https://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html

In my experience batteries last longer if used frequently. So I use the agm battery from my snowmobile in my boat during the off season. I live in Canada where the cold is very hard on batteries. I would guess that Hawaii doesn't get -40 C very often . So 1 to 2 years is what is expected for lifespan here. I also use a battery maintainer to top up batteries. It helps.

 

[alohart]

In my experience batteries last longer if used frequently. So I use the agm battery from my snowmobile in my boat during the off season. I live in Canada where the cold is very hard on batteries. I would guess that Hawaii doesn't get -40 C very often . So 1 to 2 years is what is expected for lifespan here. I also use a battery maintainer to top up batteries. It helps.

Our Swedish car was stored for 6 months each winter, so the battery was not used continuously. I usually kept the battery inside our apartment while the car was being stored so the battery didn't experience Sweden's winter temperatures.

One nice feature of AGM batteries is that their self-discharge rate is very low which makes keeping them on a battery maintainer not necessary unless the storage period is longer than a year. In fact, keeping a battery maintainer on an AGM battery could shorten its life. Just fully charge it and let it sit.

We have stored our i3 for 6 months each year since 2014. I didn't remove its AGM battery during storage and its voltage did not drop much. However, something has apparently caused it to degrade unlike my experience with the AGM battery in our Swedish car. BMW of Honolulu will be testing it on Monday, so I'll know more then.

 

[jadnashuanh]

If still connected into the car...while not huge, there is a constant load on the battery, and it will discharge. Things like the alarm and proximity sensor (looking for the remote), the clock, are always running. On the alarm, you can turn off the interior sensor, but you can't turn off the other sensors.

I don't drive my ICE all that often, and when I do, it's used for about a 1K or more at a time, but in the interim, it sits on a smart battery maintainer that understands AGM batteries...I think it has easily kept this battery usable for probably 3-4 years beyond what is more typical for that type of car. I'm approaching 6-years on my ICE's AGM battery, and the battery seems fine. The first one died at about a year with my use pattern, and after that, I started to use the maintainer on it (a Bosch C7).

A dumb battery maintainer could damage the battery...a smart one, should not.

 

[alohart]

BMW of Honolulu tested the 12 V battery in our 2014 BEV and proclaimed it to be functioning normally but they could not explain why the voltmeter that I had inserted into an accessory power port had measured voltages as low as 11.8 V when the car entered radio ready state after the doors are unlocked. They told me that the voltage at the power port isn't an accurate measurement of the voltage at the 12 V battery terminals. I don't agree, so I decided to measure the resting voltage directly across the 12 V battery terminals and then monitor the voltage when the car enters radio ready state due to my clicking the unlock button on my fob.

I recorded a short video of this test. I measured a resting voltage after our car had been parked for ~24 hours of 12.51 V which is reasonable. The longer our car is parked, the lower the 12 V battery's resting voltage. I then pressed the unlock button on my fob (the unlocking sound is audible in the video). Immediately, the voltage began dropping. Within a few seconds, the voltage dropped below 12.0 V before the DC-DC converter turned on (an audible clunk sound). The voltage immediately climbed to ~14.2 V which is normal for the charging voltage of the DC-DC converter. These voltages agree with those measured by my voltmeter at an accessory power port.

Should the voltage of the 12 V system drop so precipitously as an i3 enters radio ready state? The voltage of a 20 Ah battery would drop if the 12 V system is demanding so much power that the 12 V battery is incapable of providing the power without its voltage dropping or if the capacity of the 12 V battery is considerably lower than 20 Ah. A healthy 20 Ah battery at 77º F can power a 12 V starter motor without its voltage plummeting, so it's difficult for me to believe that various controllers booting could require as much power as a starter motor. Does this behavior seem normal?

I'm questioning how BMW of Honolulu tested our 12 V battery. If it has deteriorated as much as I think it has, an old-fashioned load test would have detected a weak battery. The Service Invoice states that the mechanic "connected ISID and found no faults related to" a weak battery. What's "ISID"?

 

[Bawareca]

ISID is the BMW diagnostic system.
From what you say the condition of your battery appears to be marginal. And because these batteries fail suddenly, i would replace it if I were you.

 

[alohart]

ISID is the BMW diagnostic system.

Thanks for the explanation! If our 12 V battery is weak as I suspect, I wonder why ISID did not diagnose it as weak.

From what you say the condition of your battery appears to be marginal. And because these batteries fail suddenly, i would replace it if I were you.

It is still under warranty, so I should not have to buy a replacement myself.

So far, I have been unable to convince BMW of Honolulu that our battery is marginal. Today, I sent my service advisor a link to the video and a description of the test I performed. I hope that this will result in further testing by BMW of Honolulu.

 

[Bawareca]

The car itself will not report the battery is getting weak until an undervoltage condition has been recorded. It may not happen in a normal daily use, but if you leave the doors opened and the music on with the ignition off, it will happen.

 

[alohart]

Today, I sent my service advisor a link to the video and a description of the test I performed. I hope that this will result in further testing by BMW of Honolulu.

The shop foreman replied:

"So I took a look at the video and this is in fact normal behavior of an I3. Prioir to the High voltage coming online all of the electrical load involved with the "wake up" process of the vehicle is taken from the 20AH 12v battery. Due to the spike in current from all of the control units waking up at the same time it can and will cause a healthy 12v battery to dip below 12v for a period of time. That being said this car has the advantage of managing battery state of charge whether or not the vehicle is turned on, hence why they can get away with such a small battery. The vehicle is monitoring not only the state of charge of the battery but also the state of health of the battery on a continual basis, meaning that if the car deems it necessary it can kick on the high voltage and charge the 12v battery without any user input. It seems you are very knowledgeable about not only your vehicle but electronics as well, I think part of the confusion may be the term "radio ready". In reality the car is waking up the majority of the control units in preparation for someone to turn the vehicle on and want to drive. This gives it time to do a "pre-flight check" prior to ignition on."

If the behavior I've noticed is normal, the low resting voltage that I observe doesn't seem normal and could reduce the life of the 12 V battery. I asked the shop foreman whether this might be due to how little we drive which might not provide enough 12 V battery charging time. He didn't respond. I would like to attach an external charger to top up the low 12 V battery occasionally, but I don't want to damage the electrical system. I would rather not disconnect the 12 V battery before charging it. I can't see how using an external charger could damage anything if the high-voltage disconnect is disconnected. Any thoughts or suggestions?

 

[Bawareca]

Another incorrect statement and lack of knowledge from a factory trained personnel.
-Once you open the car, or wake it up, only some of the modules will wake-up and the load on the battery will not be that high. In fact, the current drawn from the control modules should be under 1A. If the car is equipped with non-led interior lights that would be the biggest load.
There will be a substantial load when the ignition is turned on, but then the DC/DC inverter will be activated and 14V supplied, so the battery is not under load anymore.
-EME will monitor the state of charge and health of the 12V battery, but will not throw any kind of message that it has to be replaced. I may be wrong here, but i have never seen any message in a BMW prompting to change the battery.
-The DC/DC inverter will not be activated when the 12V voltage goes low, except if the car is connected to an EVSE.
If I were you, i would just leave the car open, with the ignition off for a while until some undervoltage codes are stored in various control modules. There will be nothing more the "foreman" could say.

 

[alohart]

Another incorrect statement and lack of knowledge from a factory trained personnel.

Thanks for your comments! I was surprised that controllers booting could consume so much power that the 12 V battery's voltage would drop as much as I observe. Apparently, that's not true.

If I were you, i would just leave the car open, with the ignition off for a while until some undervoltage codes are stored in various control modules. There will be nothing more the "foreman" could say.

I'll continue monitoring the 12 V battery's voltage. It seems far more likely that its voltage would drop below the level that allows the controllers to boot while it is parked in our parking space than when out and about. If this happens, plugging in our EVSE should allow the DC-DC converter to recharge the 12 V battery enough to start the car and drive to BMW of Honolulu. It seems that BMW of Honolulu isn't very proactive about replacing a weak 12 V battery and prefers to wait until an i3 won't start before acting.

 

[EVBob]

We are on 12v battery #3 in less than a year for our second i3 (replaced during CPO process in Jan, replaced again in April, replaced again today)
This particular i3, we drive everyday and have put 10K miles on it during our 7 months of owernship....

The service tech tried to pawn off that the i3's batteries die when the car is not driven enough and replacing it was sufficient...I told the service advisor it is driven everyday and reaffirmed this is battery #3 in less than a year, and in this instance the 12v died 20 minutes after it was driven (taking kids to the playground) - it should have been charged while driving. the service advisor is going back to the service tech and inform them to find the true cause....no one can have the luck of having three new 12v batteries going bad in less than a year...suspecting something going on with the dc-dc converter or how the car maintains the 12v batteries....but I guess we'll see....

...A little disappointed at BMW service that they would just let this fly.