12V battery step by step and preventing errors

[johnheddy]

I recently had my 12V battery die on me while 320 miles away from home on a trip. Ended up having to "jump start" my i3, and drive directly to dealership to get it changed out. They said it would take 1.5 hours and cost $500 to $550. After waiting, they told me they sold the last battery that morning, gave me a loaner and I picked it up 2 days later. They charged $460.

BUT... If they could take a fresh battery out of the box and install in 1.5 hours... Do they have a test mode or similar that they use to tell the car to engage the DC/DC converter and charge up the battery? They didn't seem to have much time to charge it up properly if the overall service was only 1.5 hours.

 

[johnheddy]

Also, when I picked up the car, the interior was all fogged up like the car had been left running for an extended period of time with no defroster running. If they had just parked it and left it off, it wouldn't be like that.

 

[JoeCool88]

I'm just thinking about putting a small standard 12V battery in the front trunk, and connect it in parallel to the dying or dead vehicle battery, to e. g. bridge the time until getting a replacement. Has someone experience in doing so or any theoretical or practical objections?

 

[EvanstonI3]

I'm just thinking about putting a small standard 12V battery in the front trunk, and connect it in parallel to the dying or dead vehicle battery, to e. g. bridge the time until getting a replacement. Has someone experience in doing so or any theoretical or practical objections?

That is not a good idea. The failing/dead 12v battery will suck all the juice out of other battery very quickly.

 

[robthebold]

That is not a good idea. The failing/dead 12v battery will suck all the juice out of other battery very quickly.

Done that. Once.

 

[Simoni3]

just fit a blue tooth voltage sensor
once the V drops below 12.2 V at any time, replace it, at around 5 yrs / 70k miles = no hassle

 

[Chris22104]

So where is the cheapest place to buy a good replacement?

 

[TheAirman]

https://www.amazon.com/gp/product/B07CR4JTZR/

Keep one on the shelf in the garage.

 

[alohart]

https://www.amazon.com/gp/product/B07CR4JTZR/

Keep one on the shelf in the garage.

Did you have to modify the screw-on SAE battery posts to fit this battery?

 

[EvanstonI3]

Did you have to modify the screw-on SAE battery posts to fit this battery?

Nope. I’ve installed this battery on my neighbors 2019 and the OEM terminal adapters fit perfectly. There is a vent hole at the rear but it needs to be drilled or reamed out to accommodate the original vent tube fitting.

 

[johnheddy]

Saw video on using i3 to run an inverter as emergency power. It said to fasten drivers seat belt while outside car, put car in park (on), turn lights and radio off, and the car would provide 12v that you can run the inverter from. IE DC/DC converter will be on.

That could be used to charge a new 12V battery in the car if it was not 100% charged before it is installed. The 12 V battery charges from the DC/DC converter.

 

[johnheddy]

I think that is what the dealer did when they installed my battery.

 

[alohart]

Saw video on using i3 to run an inverter as emergency power. It said to fasten drivers seat belt while outside car, put car in park (on), turn lights and radio off, and the car would provide 12v that you can run the inverter from. IE DC/DC converter will be on.

That could be used to charge a new 12V battery in the car if it was not 100% charged before it is installed. The 12 V battery charges from the DC/DC converter.

For the DC-DC converter to be on, the HV disconnect must be connected. Yet BMW's recommendation is to disconnect the HV disconnect when changing the 12 V battery, presumably to avoid the potential of short-circuiting the DC-DC converter should the positive 12 V battery cable clamp touch ground or the negative cable clamp. The DC-DC converter is part of the EME, the i3's most expensive electronic module, so I wouldn't want to risk damaging it.

 

[TheAirman]

What, if anything would need reset? Would you lose any coding? Or just radio, climate settings?

 

[alohart]

What, if anything would need reset? Would you lose any coding? Or just radio, climate settings?

I assume that you're asking what would happen if the 12 V battery were disconnected. I've disconnected the 12 V battery 8 times for periods of 3 to 9 months each time with no loss of coding changes or driver profiles including entertainment system presets. I always back up driver profiles to a USB flash drive using an iDrive command to protect against a potential loss which has never happened. I've only reset the date and time which isn't strictly necessary if one's i3 automatically syncs its date and time via the mobile data network.