12V battery step by step and preventing errors

[eXodus]

I got the 12V battery change ahead of me and wanted to put together a writeup how to get it done correctly the first time.
Watched every Youtube on that topic and read all threads here with "12v" in the title.

0. Day before - Charge new 12V battery all the way up, make sure you don't have to go anywhere for the next 2 days.
1. Park i3 somewhere where you can charge it
2. Open charging flap.
3. Fully charge the traction battery
4. Disconnect the J1772 charger, open Windows and leave the charging flap open !!
5. Open the frunk, wait 20-30 minutes until the car is fully shut down (all lights on the dash are off) and disconnect the high voltage disconnect in the frunk area.
6. remove the frunk insert to get to the 12v battery
7. Remove the 12V battery
8. Switch the terminal posts from old to new battery
9. Install new battery (tighten down those posts)
10. Wait for at least 20-30 minutes until the car full shuts down. (it might start on it's own then 12v was reconnected)
11. Reconnect the high voltage disconnect
12. Install the frunk
13. Open the door, start the car
14. Register battery (Bimmerlink)
15. In case of Zero or low range - Plugin J1772 overnight

Anything else I'm missing? The open windows and charging flap - is because some people had trouble getting back into the car or getting the flap open after a 12V replacement.

 

[alohart]

I've replaced the 12 V battery in our former 2014 i3, but I've done something that the car can't distinguish from having its battery replaced: I've disconnected the 12 V battery 6 times for 3 to 9 months each time as one step in storing our i3 while we travel. I have never experienced any problem when reconnecting the 12 V battery. I think the key is connecting a fully-charged battery. Low battery voltage seems to be the source of the problems that many have experienced, so not allowing an old battery's voltage to drop too much before replacing it (not always possible) and fully charging its replacement are probably the most important factors.

I've never fully charged the battery pack before disconnecting the 12 V battery or replacing it. In fact, I've purposely stored our i3 with the charge level at ~50% to reduce the cell degradation rate. Fully charging the battery pack before changing the 12 V battery certainly won't hurt, but not charging it shouldn't matter, either.

Your step 5 is important. I wonder how many wait until the HV system shuts down before disconnecting the HV disconnect. The concern is that some HV process could suddenly be interrupted when the HV disconnect is disconnected.

I don't think that step 10 is necessary because the HV system can't turn on when the HV disconnect is disconnected. However, waiting 30 minutes won't cause any problem.

One additional precaution is to make sure the doors aren't locked prior to disconnecting the 12 V battery. If the doors are locked, the burglar alarm is armed, and the very loud siren will sound the instant the first battery cable is disconnected. Scared the crap out of me once

 

[eXodus]

Thanks for the input.

So step 3 - charge to at least 50% ?

Step 10: from what I read - when the 12V system is already running - without the HV System, it's in a error state already. Then you activate the HV system and computers don't talk to each other. If you wait until the 12V is off - to then reconnect the HV system - then all computers wake up together later. That might save you step 15.

Ok leave doors unlocked is a good hint. Haven't see that yet, added to step 4.

Update list Version 2:

• 0. Day before - Charge new 12V battery all the way up, make sure you don't have to go anywhere for the next 2 days.
  1. Park i3 somewhere where you can charge it
  2. Charge the HV traction battery to at least 50%
  3. Disconnect the J1772 charger leave the charging flap open !!
  4. Open Windows and leave doors unlocked
  5. Open the frunk, wait 20-30 minutes until the car is fully shut down (all lights on the dash are off) and disconnect the high voltage disconnect in the frunk area.
  6. remove the frunk insert to get to the 12v battery
  7. Remove the 12V battery
  8. Switch the terminal posts from old to new battery
  9. Install new battery (tighten down those posts)
  10. Wait for at least 20-30 minutes until the car full shuts down. (it might start on it's own then 12v was reconnected)
  11. Reconnect the high voltage disconnect
  12. Install the frunk
  13. Open the door, start the car
  14. Register battery (Bimmerlink)
  15. In case of Zero or low range - Plugin J1772 overnight

 

[alohart]

So step 3 - charge to at least 50% ?

No, I don't think the charge level matters when replacing the 12 V battery. I stored our i3 at a 50% charge level purely to reduce the cell degradation rate.

Step 10: from what I read - when the 12V system is already running - without the HV System, it's in a error state already. Then you activate the HV system and computers don't talk to each other. If you wait until the 12V is off - to then reconnect the HV system - then all computers wake up together later. That might save you step 15.

I've never waited after connecting the 12 V battery before connecting the HV disconnect. Maybe I was just lucky, but I have had no problems. To be safe, waiting for the 12 V system to shut down certainly couldn't hurt and might avoid problems.

The official BMW procedure for replacing the 12 V battery includes waiting until the HV system shuts off before disconnecting the HV disconnect, but doesn't include waiting for the 12 V system to shut off before connecting the HV disconnect.

This procedure includes a final step which I don't understand and have never performed:

"Carry out a double terminal change (press the START-STOP button four times and maintain a pause of one second each time after having pressed the button)"

Do you understand what that does?

 

[eNate]

When I changed my last car's battery – it was an Audi allroad – I connected a 12 volt power supply to the jumper blocks to keep the systems alive during the swap.

I was imagining I'd try to do something similar with the i3 when the time comes, to avoid any problems, except that the i3 has no jump points, and attaching loose little battery minder clamps to the car's free-swinging battery cables doesn't sound practical or smart.

I'll keep this post in mind.

 

[eXodus]

"Carry out a double terminal change (press the START-STOP button four times and maintain a pause of one second each time after having pressed the button)"

Do you understand what that does?

A double terminal in electrical speak might be a contactor / relay. When everything is without power the computers might have forgotten in which state the relay currently is. When you build low draw infrastructure - relays are actuated once and then lock in place - not like regular relays which are constantly energized to be hold either closed or open.

That procedure might be a relearn for the computers to know what direction the switches are pointing. But that's a very vague guess from me My Chevy clickers through all it's relays when the battery was disconnected for a long time.

Like, so like - ok that's on - that's off - I remember

 

[EvanstonI3]

The i3 has "jump points" in the rear, under the access panel:

I was going to "jump" the car as well when I changed my 12v, but did not, and the only "reset" I noticed was that the Trip odometers went back to zero. I didn't even have to reset the date/time. Everything else stayed the same, Profiles, Pre-Sets etc.

 

[BL5]

I’ve replaced 12V batteries in both my 2015 & 2017. When I replaced 2015, it was a 36hour battle! 2017 took me an hour after charged up.

Last Friday by 2017 gave me a drivetrain error, I knew it was the 12V. Fortunately it was parked in the garage and I have another car. I didn’t have time to get a REMY, so paid $233 from dealer. First thing I did was put replacement battery on trickle charger, it needed 15 hours to top off. I had zero issue starting up 2017, registered battery, back on the road baby!

Couple things for anyone with a 4+ year old battery. Both mine went out around 5yr mark.
1. You will get no notice it’s about to go out.
2. BMW i3 is very sensitive to the voltage on your 12V
3. If your car sat for a while with a dead 12V, be prepared for a bunch of errors. It took a bunch of attempts to clear all these errors (2015)
4. Make sure that replacement battery is trickled charged before replacing. Again the BMW i3 is very sensitive around that 12V’s battery voltage, and won’t start unless it’s fully charged
5. If your i3 is 4-5 years old, I’d have a battery on hand stored in the garage ready to go.

 

[rlbouah]

Did the drive train error go away after the battery was changed?

 

[alohart]

5. If your i3 is 4-5 years old, I’d have a battery on hand stored in the garage ready to go.

I've followed this advice when we owned our previous 2014 i3 (original battery lasted over 7 years) and our current 2019 i3 that we bought used in 2022 (original battery lasted just 4 years). Because I had a fully-charged replacement battery on hand in both cases, I was able to replace both quickly and without any drama.

 

[jcallum]

I have a 2018 i3 and I am now on my 4th 12v battery. It seems to fail after about 12-18 months. The dealer says the reason for this is that I am not driving the car enough! It has about 20,000 kms on it so I am only averaging about 4,000 km per year. I think that I am going to adhere to that advice to keep a spare battery in the garage.

 

[tongsli]

I have a 2018 i3 and I am now on my 4th 12v battery. It seems to fail after about 12-18 months. The dealer says the reason for this is that I am not driving the car enough! It has about 20,000 kms on it so I am only averaging about 4,000 km per year. I think that I am going to adhere to that advice to keep a spare battery in the garage.

I wonder if it is not getting enough of a charge from the HV battery? I assume you keep it plugged in, do you keep the HV battery charged up to 100% and how often? I too do not drive that much so this is of concern to me as well.

 

[tongsli]

Has anyone tried using this type of OBDII connection? Doesn't seem necessary

https://www.amazon.com/DXAEOBD-Professional-Battery-Charger-Maintainer/dp/B09Y7L64LL

 

[jcallum]

I wonder if it is not getting enough of a charge from the HV battery? I assume you keep it plugged in, do you keep the HV battery charged up to 100% and how often? I too do not drive that much so this is of concern to me as well.

I don't keep it plugged in. I only plug it in when the battery falls below 50%. In any event that wouldn't help charge the 12v battery because, as I understand it, the 12v battery is only charged when the car is being driven and it is a trickle charge relay so you have to drive for a while to get the charge up to 100%.

 

[eNate]

the 12v battery is only charged when the car is being driven and it is a trickle charge relay so you have to drive for a while to get the charge up to 100%.

Refer to @EvanstonI3's post here for his plot of the i3's 12 volt charging behavior. The car does not need to be driven for a low voltage condition to be detected and changed.

Post in thread '12 volt battery in later i3s--watch out' https://www.mybmwi3.com/threads/12-volt-battery-in-later-i3s-watch-out.17711/post-76293

 

[alohart]

Has anyone tried using this type of OBDII connection? Doesn't seem necessary

https://www.amazon.com/DXAEOBD-Professional-Battery-Charger-Maintainer/dp/B09Y7L64LL

In U.S. i3's, leaving a dongle plugged into the OBD port results in the burglar alarm being activated after a certain period of time. This can be disabled by making a coding change. However, as you wrote, maintaining the battery via the OBD ports seems unnecessary.

 

[alohart]

I have a 2018 i3 and I am now on my 4th 12v battery. It seems to fail after about 12-18 months. The dealer says the reason for this is that I am not driving the car enough! It has about 20,000 kms on it so I am only averaging about 4,000 km per year. I think that I am going to adhere to that advice to keep a spare battery in the garage.

During the pandemic, our i3 was driven only ~100 miles (~160 km) per month. That was insufficient to offset the vampire 12 V loads and to keep the 12 V battery's charge level high enough to avoid the "excessive discharge while parked" message from being displayed. When that happened, I fully charged the 12 V battery using a battery charger after disconnecting the HV disconnect. I even installed a charging harness on the battery's terminals so that it would be easier to connect the charger. That worked well. That battery lasted for over 7 years before failing.

 

[tongsli]

In U.S. i3's, leaving a dongle plugged into the OBD port results in the burglar alarm being activated after a certain period of time. This can be disabled by making a coding change. However, as you wrote, maintaining the battery via the OBD ports seems unnecessary.

thanks Alohart, I was actually thinking during a battery change. But I don't think it's necessary in that case either.

 

[robthebold]

I couldn't make any sense of the "excessive discharge while parked" warning when I got it. I wondered if I left accessories on somehow, except that I didn't see any suggestion that the auto-off wasn't working. In retrospect, the only times I saw the warnings were in the weeks leading up to the battery dying.

 

[Gonville]

I don't keep it plugged in. I only plug it in when the battery falls below 50%. In any event that wouldn't help charge the 12v battery because, as I understand it, the 12v battery is only charged when the car is being driven and it is a trickle charge relay so you have to drive for a while to get the charge up to 100%.

The 12v is charged when the HV is being charged. Could be why the poor things are dying if they are not left plugged in at least some of the time and mileage is relatively low?