12 V battery replacement suggestions needed

[Srivenkat]

Also, the high-voltage disconnect should probably be opened before disconnecting the 12 V battery, so using an autodisconnect switch might not work well. The BMW Technical Information System suggests that an i3 software update in 2014 might have removed this requirement, but I wouldn't risk it.

Autodisconnect would be quite the same as a dead battery, right, or is there a pertinent difference I am missing.

 

[alohart]

Autodisconnect would be quite the same as a dead battery, right, or is there a pertinent difference I am missing.

Autodisconnect would be an instant loss of 12 V whereas a dying battery is usually gradual. Why this might matter is that the i3's high-voltage system requires a 12 V controlling circuit to be powered. BMW Technical Information System documentation warns against this circuit losing power while the high-voltage system is active. It's not clear to me whether this was fixed with an i3 system software update in 2014 or whether the high-voltage system needs to be inactive when its 12 V controlling circuit loses power. This normally occurs when the high-voltage disconnect is opened, but autodisconnect disconnecting would have the same effect.

I don't understand the relationship between the 12 V and high-voltage systems. However, there might be reason to be careful when modifying how the 12 V system works.

 

[jadnashuanh]

The computers run on the low-voltage...without the 12vdc battery there as a buffer and supply, most anything else doesn't work, including the TOD clock and the cellular connection. I'm not sure how much else is in NVM, and losing the 12vdc may lose all of your preferences and item storage, too.

 

[oldman42]

I left the i3 (2014, BEV) in the driveway (unplugged). I took the ICE on an overnight trip, and when I returned today and I unlocked the i3 with the key fob, and the alarm goes off and I can't turn it off. I grabbed both key fobs, and mashed all the buttons. Nothing. Car doesn't powerup either. Screens remains blank. If I let it sit, the alarm will shut off, but as soon as I open the door, the alarm goes off again. Also worth noting I was getting the "discharge while stopped" message about two weeks ago, but went away. After some searching, sounds like my 12V is done. Couple of questions:
1) Any way to prevent the alarm from going off?
2) Can the 12V be jumped with one of those battery pack jumpers? To move the car into the garage or to the dealership.
3) Would the 12V battery respond if I hook it up to a Battery Tender for a day or so?
4) Would plugging in the HV battery help?

Thanks!

 

[alohart]

1) Any way to prevent the alarm from going off?

It has its own power source so that a thief can't disconnect the 12 V battery to disable the alarm. I don't think that it can be disabled which would be a security risk.

2) Can the 12V be jumped with one of those battery pack jumpers? To move the car into the garage or to the dealership.

There's a risk of damaging the DC-DC converter if the battery is jumped while the high-voltage system is on. If the high-voltage system is off, an i3 can't enter drive ready state, so it's a Catch-22.

3) Would the 12V battery respond if I hook it up to a Battery Tender for a day or so?

Depends on the condition of the battery. Seems like it failed quickly which suggests an internal short-circuit or some other problem that might prevent it from holding a charge. It's certainly worth trying but only after the high-voltage disconnect has been opened (disconnected).

4) Would plugging in the HV battery help?

There's a circuit that will charge the 12 V battery when an EVSE is plugged in and the 12 V battery is dead. So that would be worth trying as well. Not necessary to disconnect the high-voltage disconnect.

 

[jadnashuanh]

Check with the dealer's service department to be sure, but I read somewhere that after a certain software build, you don't need to disconnect the HV battery when charging the 12vdc battery. It's probably better to do that, but to get into the vehicle, you may need the key. Popping out the cover to get to the driver's door key slot, read the manual.

The 12vdc socket in the vehicle is not connected constantly, so you can't use that...you'd have to go to the 12vdc battery in the front.

There's supposed to be a trickle charger function if the computer won't come one, but it's slow, and depending on the health of the battery, may not work, but is the easiest thing to try. I'd figure at least overnight, and the colder it is, the weaker a lead-acid battery gets, even an AGM version.

 

[oldman42]

To follow up on my previous post, I tried hooking up my ICE to the i3 via jumper cables. Unfortunately, the alarm continued to chirp, but the headlights started flashing and the horn was honking with the alarm. Some lights and error messages popped up on the screens, so there might have been something going on. But, the car wouldn't start, HV battery didn't initiate. Since it was 8pm and the car alarm was blaring, I decided to call it a night. Again, closing the frunk and the doors, the alarm stops after a few minutes.
Being over 6 years old, I am pretty sure I'm due for a new battery. I sourced a new 12V from a local BMW. I couldn't wait for shipping from an online retailer. I would recommend calling around (if you live in an area with multiple dealerships) since I was quoted different prices. As I mentioned in my previous post, my alarm would go off as soon as I opened the door (I unlocked the door with the key since the keyless entry wasn't working). So, with the alarm chirping, I manually popped the hood, took out the cubby, flipped the HV disconnect, took off the bracket, disconnected negative, then the drain hose, and alarm stopped when I disconnected the positive terminal connection. Overall, not too difficult, just wish I wore ear protection while I did this. Picked up the new battery. Plugged up the new battery to a Battery Tender and let it charge overnight. Installed the new battery the next morning and as soon as I connected the negative terminal, lights come on and screens lit up. It's alive! Only thing I needed to do is correct the time and date. Other than that, seems like nothing happened. Even my radio station preset were saved. I did not do the battery registration, still debating if I need to do that. So, in summation, as soon as "discharge while stopped" message appears, and your 12v battery is 4-5+ years old, get the battery replaced before your i3 becomes a brick. Thanks to the MyBMWi3 community for your feedback!

 

[rcy001]

Does the ‘increased battery discharge’ message only appear during startup? I am not the one driving it daily. Is it saved in some menu? I could not find it.

Also, there is BMW’s Battery Guard as part of the Teleservices package which is a standard subscription according to my I3’s Connected Drive portal. This should alert the dealer of impending 12 volt battery failure. Is this not present on non-European versions? This should be the best way to avoid a bricked I3.

 

[oldman42]

Does the ‘increased battery discharge’ message only appear during startup? I am not the one driving it daily. Is it saved in some menu? I could not find it.

Also, there is BMW’s Battery Guard as part of the Teleservices package which is a standard subscription according to my I3’s Connected Drive portal. This should alert the dealer of impending 12 volt battery failure. Is this not present on non-European versions? This should be the best way to avoid a bricked I3.

For me, the message appeared only at startup. And it can easily be cleared off the screen like nothing happened. And it only appears after being parked for an extended period of time (overnight or longer). It would go away and wouldn't see it for several days as well. So I disregarded it, and after about 2 weeks, it bricked. If your 12V is about 4-5 years old, I'd think about getting it replaced. Nothing worse than scrambling to get a battery replaced after it has died. And considering you can't jump the i3, its more of a pain. Good luck.

 

[Anonymous]

Also, there is BMW’s Battery Guard as part of the Teleservices package which is a standard subscription according to my I3’s Connected Drive portal. This should alert the dealer of impending 12 volt battery failure. Is this not present on non-European versions? This should be the best way to avoid a bricked I3.

Not available on USA cars, that I'm aware of. As I understand it, will alert you on a battery drain, like if you left your lights on, but on a slowly dying battery it alerts your dealer when the battery voltage falls below a set parameter, but the alert is only sent the next time the car is started - and the alert is to a Dealer, who may or may not contact you promptly. So if the battery is weak, but the voltage is above the 'fail-safe' voltage, you park it for a few days and the battery dies and won't power up the car. No alert, and a dead battery. Most of the time it should work to alert you, but not always. If a battery is five plus years old, I'd proactively replace it. I just replaced the 12v in my 2015 - original battery. The old battery I took out still tests as 'Good' and holding a charge, but in talking to a local independent BMW mechanic, 5 to 6 years is normal end-of-life on the 12v batteries, with the i3 often closer to 4 years in harsher (hot/cold) climate.