12V battery

[MarkH]

It hasn't happened (yet) but I'm wondering ....

What happens when the 12V battery fails?
Does it leave you unable to start the car (and drive to a dealer) - or what?

 

[jadnashuanh]

All of the computers, lights, etc. are powered by the 12vdc system. The 12vdc battery gets recharged during operation once the high voltage circuit turns on. If the 12vdc battery dies, and you plug in an EVSE, the car won't immediately start to charge since the controls won't be active, but there's a backup trickle charger to the 12vdc battery that will try to bring it back up to a high enough value to then run the car. But, in the interim, you have a big brick unless you change the battery. There's a very special procedure to try to recharge the battery...you must disconnect the high voltage first, or you'll end up damaging things or yourself.

Note, the charging logic in BMWs adjusts based on the type, size, and age of the battery installed. When you change to a new one, even if it's the same in every way (except being new), it will be treated as if it were an old one based on the timer. So, you need to reprogram the logic to restart the timer, and treat the battery as a new one. Should you change the type or size, that would need to be updated as well, or you could damage the new battery.

Some time, the car is too smart...

 

[MarkH]

So, if the trickle charge gets it back up so I can start the car, will the car run OK until the next time I stop and try to re-start it?
ie, do I have just one shot at driving to the nearest BMW shop - 100kms away for me?

How long are people getting out of their 12v batteries before they die?
What sort of warnings do they give if they are on their way out?

 

[alohart]

So, if the trickle charge gets it back up so I can start the car, will the car run OK until the next time I stop and try to re-start it?
ie, do I have just one shot at driving to the nearest BMW shop - 100kms away for me?

I suppose it depends on why the 12 V battery was so discharged. It's pretty difficult to discharge the 12 V battery because the DC-DC converter is very aggressive about charging it, and most 12 V accessories seem to turn off automatically a few minutes after shutting down an i3. I suppose leaving parking or clearance lights on could discharge a weak 12 V battery unless leaving these lights on could cause the DC-DC converter to maintain the 12 V battery's charge. Also, parking an i3 for several weeks without driving it could discharge the 12 V battery too much to start the car.

I suspect that most cases of the 12 V battery's charge level being too low to boot an i3's controllers are due to a failing or failed 12 V battery. If the failure mode prevents the 12 V battery from holding a charge or reaching full charge voltage due to a bad cell, the trickle charge that occurs when an EVSE is plugged in and actively charging would likely be insufficient to allow an i3 to start.

Personally, if our 12 V battery discharged too much to start our i3 while it was parked in our apartment parking space, I would disconnect the high-voltage disconnect and the 12 V negative battery cable so that I could attach a 12 V battery charger for a few hours in case the 12 V battery had gradually become discharged from being parked so much and driven so little which could occur in our case.

How long are people getting out of their 12v batteries before they die?
What sort of warnings do they give if they are on their way out?

I believe that our original 12 V battery was manufactured in May, 2014. Our BEV was manufactured on 1 August 2014. We bought it on 5 November 2014. Its original 12 V battery continues to work normally with no warning that it's about to fail. However, it has never been exposed to extreme temperatures and has led an easy life considering that it has been disconnected for a total of 2 years while our i3 was in storage.

 

[eNate]

This is the BS thing with these "smart" coded battery systems -- they don't work!

From what I've been reading about the 12v battery on this and other i3 forums, you can expect 3 to 4 years of service from it.

Rather than the system monitoring the battery's performance and providing a warning that it's nearing time for replacement, all the odd symptoms that are topics of the other "dying 12v battery" posts begin making appearances.

It's not an i3-specific problem. My neighbor's BMW Z4 stranded him without warning in exactly the same way. And after dropping in a brand new 12v battery, his car was relegated to limp mode until he took it in to get it coded. Bunch of malarkey. Hooey, I tell ya!

With my Ford, I can accept that when the battery dies without warning, that's that, because the drop-in replacement doesn't require any back-end programming or resetting. Unfortunately with HID and LED headlights and pushbutton starting, all of the tell-tale signs of a dying battery are gone.

And with my previous car, an Audi with a coded battery, I skated around all the shenanigans by connecting a 12v power supply to the car to keep it alive while I swapped batteries. Didn't code it, and the car didn't skip a beat because of it.

 

[MarkH]

I would disconnect the high-voltage disconnect and the 12 V negative battery cable so that I could attach a 12 V battery charger for a few hours

Since I have a 12V charger, this sounds like a reasonable solution to getting going again - even if it's just so I can get the car to a dealer to replace the battery.

Is there a link to how to disconnect the high-voltage??

 

[alohart]

Is there a link to how to disconnect the high-voltage??

This describes how to disconnect the high-voltage disconnect which is a step in this description of how to charge the 12 V battery.

A note at the top of the battery charging procedure states that disconnecting the high-voltage disconnect isn't strictly necessary for i3's whose system software isn't a very early version. However, disconnecting the high-voltage disconnect is so easy that I always do it before disconnecting the 12 V battery which I have done at least 4 times preparing our 2014 BEV for storage. I have never had any problems after reconnecting the 12 V battery.

 

[MarkH]

Thanks for that reply, Art.
Woah! It all looks pretty intimidating :?
My BEV is 2016 - maybe we don't need to disconnect the HV?

You say you disconnect the 12V before putting the car in storage.
We will be leaving the car unused for two months next year. Is that long enough to warrant doing this?

 

[alohart]

Woah! It all looks pretty intimidating :?

It's really not. The high-voltage disconnect is easily accessible under the cover to the right of the frunk box.

My BEV is 2016 - maybe we don't need to disconnect the HV?

I don't want to risk potential damage that might occur to the DC-DC converter when a 12 V battery charger is attached to the battery terminals (some sparking is difficult to avoid) and turned on. The procedure I referenced does suggest that disconnecting the high-voltage disconnect isn't necessary when the system software version is later than that installed on early 2014 i3's.

You say you disconnect the 12V before putting the car in storage.
We will be leaving the car unused for two months next year. Is that long enough to warrant doing this?

Parking an i3 for 2 months without disconnecting the 12 V battery or leaving an EVSE plugged in would almost certainly result in a very discharged 12 V battery, maybe permanently damaged if completely discharged. This isn't unique to an i3 or even an EV. All modern vehicles have vampire 12 V loads that will discharge the 12 V battery over time.

 

[jadnashuanh]

If you left it plugged into an EVSE, over that two months, it might activate the EVSE 3-4 times, if that, but enough to keep both batteries charged. Unlike a cellphone or most other consumer battery powered devices, the car is not getting a constant charge while connected...it only turns on once the levels drop enough to warrant it while preserving the batteries.

 

[Lesterbmwi3]

My 2014 I 3 is 5 1/2 years old when my 12 volt battery will be dead? Always in heated garage in NY 17000 miles and driven daily few miles should I replaced as preventative measures now bc in every car I ever own I replaced 12 V battery s every 5 years and never have an issue Looking for advice My BMW dealer price $450 to do replacement nice ! Battery alone is about $200 Thxs

 

[alohart]

My 2014 I 3 is 5 1/2 years old when my 12 volt battery will be dead?

Impossible to predict.

Always in heated garage in NY 17000 miles and driven daily few miles should I replaced as preventative measures now bc in every car I ever own I replaced 12 V battery s every 5 years and never have an issue Looking for advice My BMW dealer price $450 to do replacement nice ! Battery alone is about $200

You have several options.

You could have your BMW dealer replace your battery in advance of it failing. This would be the most expensive option.

You could have an independent BMW mechanic replace your battery in advance of it failing. This should be less expensive than a BMW dealer.

You could buy a new AUX18L battery with various brand names like East Penn or Deka for much less than $200. There is no advantage to purchasing a BMW-branded battery (all U.S. i3's have the same AUX18L battery manufactured by East Penn Manufacturing). You could store it until your battery dies. However, if your battery dies while you're not at home, you could be stranded. This is the alternative that I have chosen.

 

[Lesterbmwi3]

Thank you for advice just happen where I live all Bmw independent shops don’t want to deal with I 3 period the dealer is only my choice is something on dash is going to show me battery is on last leg or dyes suddenly

 

[alohart]

Thank you for advice just happen where I live all Bmw independent shops don’t want to deal with I 3 period

Changing an i3 12 V battery is no different from changing the 12 V battery in any BMW vehicle. Same with changing the brake fluid. By refusing to work on i3's at all, these independent shops are leaving money on the table.

is something on dash is going to show me battery is on last leg or dyes suddenly

There can be a warning message about the battery discharging. However, it's a confusing message because it doesn't specify which battery is discharging (it's always the 12 V battery), and this message isn't displayed in all cases in which the 12 V battery is failing.

 

[jadnashuanh]

It's not a big deal to swap the 12v battery. It's not hard to recode the computer to know that it is new. It's a slight bit more complex if you decided to change the type or size of the battery. It will work without recoding, but the concept is that by treating it as new rather than an old, dying one, the new one will last longer if you tell the car about it. This is possible with various programming tools. Some places, like say Pep Boys will do it for a fee, and if you have the right tools, is easily done yourself. Last resort would be the dealer, where they'll typically charge you a bunch for it.

FWIW, when I was looking for a new battery for my ICE, the BMW dealer had the cheapest price on the battery alone, but their installation costs were excessive. I bought the battery there, then installed it myself along with coding it.

My i3 was built in April 2014, but the battery seems to be fine. I'll probably not deal with it until it starts to act funny. It sits outside, so in the winter, it can be quite cold, and it might sit there for a few days in between uses, but I generally leave it plugged into the EVSE, so it can top off the batteries when it thinks it needs to.

 

[jfran2]

After reading several horror stories on other forums, I decided to be proactive and change the battery in my 2014 i3 Rex. A new battery is around $140, and the Foxwell NT510 scan tool to code it is $155. (vs $500 for the dealer to do it.) There are several Youtubes available with good instructions on the procedure.

 

[MarkH]

If you left it plugged into an EVSE, over that two months, it might activate the EVSE 3-4 times, if that, but enough to keep both batteries charged. Unlike a cellphone or most other consumer battery powered devices, the car is not getting a constant charge while connected...it only turns on once the levels drop enough to warrant it while preserving the batteries.

My domestic charger is not smart. I usually charge the car through a timer such that it charges from about 30% to 80%.
Any idea how many minutes a day would cover the "dark" drain from the 12V battery? Would 5 minutes a day cover it?

(Then the question is whether I'm happy to leave a 10amp (240V) rated timer going for 2 months while we're away :? ....)

 

[jadnashuanh]

It's my observation that it takes the car quite awhile before the main battery's voltage drops enough to activate the EVSE. There's a moderate amount of hysteresis in it, meaning that it waits until it will need to run the charging for a bit before it turns on rather than just a little bit, frequently. Not sure how often it would turn on, but when the time came, it would take more than a few minutes to bring things back to full.

Maybe someone has monitored it a bit more closely. I haven't tested my 12vdc battery, but it seems to be functioning okay at what will be 6-years in April. I plug the EVSE in when I get home, and remove it when I leave, and my range is about the same now as when it was new, too.

I expect I'll be selling it come next summer, but that's still up in the air somewhat. I'll replace the battery if I start to see problems, but until then, leave well enough alone. The AGM battery in my ICE lasted about 7-years. Since it sat in the garage a lot, I usually kept a smart battery tender on it, which may have helped.

SOme people don't trust the engineers. I figure that they have a lot more knowledge on their system than 'generic' knowledge. There are lots of different chemical mixes in various LiOn batteries. From what I've read, that chosen for the i3 is one of the more reliable ones. I let the car figure when it needs to charge and how much. I might regret it eventually, but so far, so good.

 

[MarkH]

OK, if I'm going to be storing the car for 2 months then my best course of action is
1 - disconnect the high-voltage system from the 12V system.
2 - disconnect the 12V battery negative terminal.

Is that it?

Does everything work again on reconnection without doing anything special?

Also, if I'm needing to do this (disconnect the 12V battery) a couple of times a year, it seems it would be easier if I wired in a disconnect switch in an easily accessible place adjacent to the battery. Is there some reason that I should NOT do this?

 

[alohart]

OK, if I'm going to be storing the car for 2 months then my best course of action is
1 - disconnect the high-voltage system from the 12V system.
2 - disconnect the 12V battery negative terminal.

Is that it?

If you want to park your car with its doors locked, you need to be aware that if the doors are locked when you disconnect the 12 V battery, the burglar alarm will sound. This is particularly exciting while your head is inside the frunk disconnecting the 12 V battery So don't lock the doors until the battery has been disconnected. Then lock the passenger door from inside the car and use the physical key in your fob to lock the driver's door.

Also, it's more convenient to not close the frunk completely. If you do, you'll need to use the emergency cable to unlock it when you return because the frunk unlock button on the fob or in the driver's door jam requires 12 V.

Does everything work again on reconnection without doing anything special?

You'd probably lose your driver profiles when the battery is disconnected. Therefore, back them up to a USB thumb drive before you disconnect the 12 V battery, an iDrive command. Then after reconnecting the 12 V battery, restore your driver profiles from the thumb drive.

Also, if I'm needing to do this (disconnect the 12V battery) a couple of times a year, it seems it would be easier if I wired in a disconnect switch in an easily accessible place adjacent to the battery. Is there some reason that I should NOT do this?

I can't think of any reason not to do this. I haven't done this because I don't find disconnecting the negative cable to be very difficult, and I don't disconnect the 12 V battery more than once per year while traveling. Maybe I should look into 12 V battery disconnect options.