symonray
Posts: 70
Joined: Thu Mar 07, 2019 8:52 am

12 volt battery failure question

Fri Feb 07, 2020 10:32 am

I woke up this morning with my i3 Rex being completely dead with no remote or electrical or power functions. There was no prior warning or warning signs. All symptoms point to a failure of the 12 volt battery. I was able to open the charging port hatch with the manual release and connect my level 2 charger to the vehicle. My Juice Box Pro 40 currently shows the vehicle accepting a very low rate of charge. Does this indicate that the system is trying to recharge the 12 volt battery via a trickle charge? If so, does anyone have an estimate as to how long the process will take?

Although I have already purchased a replacement 12 volt battery, I would prefer to do the replacement myself after the power has been restored to the system so that I can use the power options to open the frunk and disconnect the charging cable before installation of the battery. Thanks.
Timothy Simonds
2017 BMW i3 Rex

eNate
Posts: 755
Joined: Mon Sep 09, 2019 5:33 pm

Re: 12 volt battery failure question

Fri Feb 07, 2020 10:46 am

I haven't seen it with my own eyes, but there is a manual hood release under a cover below the hood release button.

Sounds like you've got the right approach, though, charging the HV first and letting it recoup the 12v.
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symonray
Posts: 70
Joined: Thu Mar 07, 2019 8:52 am

Re: 12 volt battery failure question

Fri Feb 07, 2020 11:04 am

I seem to recall a post (maybe from jadnashuanh) that indicated that the vehicle's HV battery charging system has a process for recharging the 12 volt battery when needed, but I could not find the post. If so, that might explain why the car is currently accepting a charge, albeit at a very low rate.
Timothy Simonds
2017 BMW i3 Rex

eNate
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Joined: Mon Sep 09, 2019 5:33 pm

Re: 12 volt battery failure question

Fri Feb 07, 2020 1:36 pm

eNate wrote:
Fri Feb 07, 2020 10:46 am

I haven't seen it with my own eyes, but there is a manual hood release under a cover below the hood release button.

Scratch that, just got my i3 back from the shop so I went looking for the emergency hood release.

It's right where you'd think it ought to be, and thank goodness it's an actual steel cable with a pull loop, not that blue plastic mess that's used for the charging door and charging handle disconnect.

So if you ever need to manually release the latch holding down the frunk lid, "Pull Here." :)

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alohart
Posts: 2424
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Re: 12 volt battery failure question

Fri Feb 07, 2020 2:29 pm

symonray wrote:
Fri Feb 07, 2020 10:32 am
I woke up this morning with my i3 Rex being completely dead with no remote or electrical or power functions. There was no prior warning or warning signs. All symptoms point to a failure of the 12 volt battery. I was able to open the charging port hatch with the manual release and connect my level 2 charger to the vehicle. My Juice Box Pro 40 currently shows the vehicle accepting a very low rate of charge. Does this indicate that the system is trying to recharge the 12 volt battery via a trickle charge? If so, does anyone have an estimate as to how long the process will take?
In the Owner's Manual:
Charging vehicle with a discharged vehicle battery

1. Unlock the vehicle, if needed, using the integrated key, refer to page 38.
2. Secure the vehicle against rolling.
3. Manually unlock charging port flap if it is locked, refer to page 163.
4. Connect either a Level 1 or Level 2 charging cable to the household socket or the port on the charging station.
5. Attach charging cable corresponding to the charging socket connection.

Charging is started. The charging status is not displayed. Do not open vehicle during this time.

After several minutes, the vehicle is slightly charged. The onboard electronics are ready again. It is again possible to open the vehicle. The charging status as well as the charging state of the high-voltage battery can be displayed again.

Continue charging vehicle until desired range is possible.

If the vehicle battery cannot be charged, contact the service center.
If the 12 V battery is internally short-circuited or has other fatal problems such that it won't hold a charge, this procedure won't charge the 12 V battery enough to enter drive readiness state. How long the 12 V battery must be charged in this way depends on its condition.
symonray wrote:
Fri Feb 07, 2020 10:32 am
Although I have already purchased a replacement 12 volt battery, I would prefer to do the replacement myself after the power has been restored to the system so that I can use the power options to open the frunk and disconnect the charging cable before installation of the battery.
If you don't believe that something merely discharged your 12 V battery and feel that it needs replacing, I suggest forgetting about trying to recharge it. You can do everything necessary to replace the 12 V battery even with a dead 12 V battery.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

symonray
Posts: 70
Joined: Thu Mar 07, 2019 8:52 am

Re: 12 volt battery failure question

Fri Feb 07, 2020 2:52 pm

Thanks for all the insightful replies. Leaving the vehicle connected to my home charger did the trick. The 12 volt battery received enough charge to power up all the electronics and put the vehicle in a ready state, and I drove it a few miles this afternoon with no problems. I am sure the battery is on its last legs, and I have scheduled an appointment with the local dealer on Monday morning to evaluate the battery and make a warranty claim for replacement (since the 4 year warranty is still in effect). If I can get BMW to cover the battery replacement under warranty, then I will keep my new REMY battery as a spare.
Timothy Simonds
2017 BMW i3 Rex

symonray
Posts: 70
Joined: Thu Mar 07, 2019 8:52 am

Re: 12 volt battery failure question

Mon Feb 10, 2020 8:37 pm

Update—I took my 2016 Rex to the dealer today. The service tech determined that the 12 volt battery was defective (no surprise there), and the dealer replaced the battery under warranty.
Timothy Simonds
2017 BMW i3 Rex

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