Did you know there are (at least) two 12V batteries in the 45e?

RickObe · 11-21-2022, 06:48 PM

I removed the storage tray that's under the rear floor of my 45e and found there is a 2nd 12V battery under there. (And a fair amount of unused space.)

Anyone know why two 12V batteries and how they are used?

roxxor · 11-21-2022, 07:00 PM

It’s standard on all of the PHEVs from BMW, my 530e had one too. I believe that some of the electronic systems operate off of that battery when the ICE isn’t running, but don’t quote me on that. You do have to disconnect those two and disable the high voltage battery if you ever need to do electrical work on the car.

RickObe · 11-22-2022, 05:44 AM

Quote:

Originally Posted by roxxor

It’s standard on all of the PHEVs from BMW, my 530e had one too. I believe that some of the electronic systems operate off of that battery when the ICE isn’t running, but don’t quote me on that. You do have to disconnect those two and disable the high voltage battery if you ever need to do electrical work on the car.

It's well known that all accessory systems, including the starter motor, run off 12V with the ICE running or not. (The ICE doesn't have an alternator.)

But my question isn't why is there a 12V battery. My question is why are there TWO of them.

Perhaps the larger one runs the starter motor and HVAC and the smaller one runs the lower draw components. But that's just a total guess.

RickObe · 11-22-2022, 06:00 AM

P.S. There are many threads on here describing problems when 12V power is gone, and they all refer to the "the" 12V battery. That's why I was surprised to find there are two of them.

Thinking about it more, it would make sense that maybe the smaller one powers the computers and the larger one everything else. That could be a way that they try to protect power to the computer modules?

timmahh · 11-22-2022, 03:10 PM

Quote:

Originally Posted by RickObe

P.S. There are many threads on here describing problems when 12V power is gone, and they all refer to the "the" 12V battery. That's why I was surprised to find there are two of them.

Thinking about it more, it would make sense that maybe the smaller one powers the computers and the larger one everything else. That could be a way that they try to protect power to the computer modules?

Check under the passenger side strut/windshield cover.

If I recall correctly:

My 2020 40i had the large under-trunk battery and a 12V battery in the engine compartment where I mentioned.

My 2021 40i, 48v mild hybrid, has the large under-trunk battery and the 48v lithium ion battery in the engine compartment where I mentioned.

aMIC · 06-05-2023, 07:41 PM

Quote:

Originally Posted by RickObe

I removed the storage tray that's under the rear floor of my 45e and found there is a 2nd 12V battery under there. (And a fair amount of unused space.)

Anyone know why two 12V batteries and how they are used?

Hi Rick!

By any chance that you have close-up pictures of the 2 batteries?
I have a 45e MY 2023 and I wonder what is the Capacity of each 12V battery.
Thanks!

javapro · 06-05-2023, 07:57 PM

Quote:

Originally Posted by RickObe

It's well known that all accessory systems, including the starter motor, run off 12V with the ICE running or not. (The ICE doesn't have an alternator.)

But my question isn't why is there a 12V battery. My question is why are there TWO of them.

Perhaps the larger one runs the starter motor and HVAC and the smaller one runs the lower draw components. But that's just a total guess.

The HVAC runs off the high voltage hybrid battery!

eelnoraa · 06-05-2023, 08:33 PM

Quote:

Originally Posted by RickObe

It's well known that all accessory systems, including the starter motor, run off 12V with the ICE running or not. (The ICE doesn't have an alternator.)

But my question isn't why is there a 12V battery. My question is why are there TWO of them.

Perhaps the larger one runs the starter motor and HVAC and the smaller one runs the lower draw components. But that's just a total guess.

45e doesn't have 12V started motor either. the "start motor" is the EV motor running of HVB as well.

Heavy 12V loads in 45e is cooling fans for radiator, head lights, aux electric water pump ... If I have to make a wild guess, all the typical car functions are running for the large 12V battery. The small one is only for door sensors, telemetry .... the low power function when the car is in sleep mode when parked and locked.

jad03060 · 06-05-2023, 10:05 PM

Well, it's my understanding that the 45e does have a traditional starter motor, but there are two ways to start the ICE:
- regular starter motor used when stopped
- EV motor in 'tow-start' mode when moving

No 12vdc, you have a bricked vehicle as none of the computers will turn on. Once they do, the HVB can make 12vdc, but not before the 12vdc computer logic turns on.

e61it · 06-05-2023, 10:50 PM

Would it be wise to occasionally trickle charge the two 12v batteries or is the ev charge of these batteries sufficient to keep them in good shape for 4-5 years? If so does anyone know if they are linked together so that the 12v charging connection in the engine compartment will charge both of them simultaneously? Also would they both be gel and need to be charged at low level? Thanks in advance for replies.

jad03060 · 06-05-2023, 11:39 PM

They're AGM batteries, and if you use the battery charging points under the hood, yes, both batteries will be charged. There's still some questions about whether the HVB system, when the vehicle is off, charges the 12vdc batteries, but it does when you're charging them, or if you're driving, but BMW does not generally try to keep them at 100%. IMHO, an occasional use of a trickle charger is worthwhile.

The area tech rep thought it did, but wasn't sure. He said he'd get back to me, but it's been over a week now, with no response. If the system was not being used over an extended period of time, without any charging being hooked up, people have reported the HVB retained their charge which, I think, would not be true if the parasitic losses in the 12vdc system required them to be recharged during that interval, and bring the HVB level down, at least some.

RickObe · 06-06-2023, 06:02 AM

Quote:

Originally Posted by aMIC

Hi Rick!

By any chance that you have close-up pictures of the 2 batteries?
I have a 45e MY 2023 and I wonder what is the Capacity of each 12V battery.
Thanks!

This is the best res photo I have. Not sure if you can make out the specs. The right sidewell battery is easy to access; just pop out the panel on the right. To get to the one under the tray, you have to remove 8 or so pop clips, then the tray easily slides out.

11-21-2022, 06:48 PM	#1
RickObe Second Lieutenant 93 Rep 213 Posts Drives: 2023 X545e Join Date: Jun 2022 Location: Western Pennsylvania iTrader: (0)	Did you know there are (at least) two 12V batteries in the 45e? I removed the storage tray that's under the rear floor of my 45e and found there is a 2nd 12V battery under there. (And a fair amount of unused space.) Anyone know why two 12V batteries and how they are used? Attached Images __________________ X5 xDrive 45e 2023 / Mineral White / Tartufo / Anthracite-Brown Poplar
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11-21-2022, 07:00 PM	#2
roxxor Major 1145 Rep 1,147 Posts Drives: 2024 iX50 Join Date: Feb 2012 Location: Florida iTrader: (7)	It’s standard on all of the PHEVs from BMW, my 530e had one too. I believe that some of the electronic systems operate off of that battery when the ICE isn’t running, but don’t quote me on that. You do have to disconnect those two and disable the high voltage battery if you ever need to do electrical work on the car.
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11-22-2022, 06:00 AM	#4
RickObe Second Lieutenant 93 Rep 213 Posts Drives: 2023 X545e Join Date: Jun 2022 Location: Western Pennsylvania iTrader: (0)	P.S. There are many threads on here describing problems when 12V power is gone, and they all refer to the "the" 12V battery. That's why I was surprised to find there are two of them. Thinking about it more, it would make sense that maybe the smaller one powers the computers and the larger one everything else. That could be a way that they try to protect power to the computer modules? __________________ X5 xDrive 45e 2023 / Mineral White / Tartufo / Anthracite-Brown Poplar
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06-05-2023, 10:05 PM	#9
jad03060 Major General 3206 Rep 6,872 Posts Drives: X5 45e Join Date: Aug 2018 Location: NH iTrader: (0)	Well, it's my understanding that the 45e does have a traditional starter motor, but there are two ways to start the ICE: - regular starter motor used when stopped - EV motor in 'tow-start' mode when moving No 12vdc, you have a bricked vehicle as none of the computers will turn on. Once they do, the HVB can make 12vdc, but not before the 12vdc computer logic turns on.
	Appreciate 0 Quote

06-05-2023, 10:50 PM	#10
e61it Private First Class 85 Rep 181 Posts Drives: bmw 545it Join Date: Jan 2021 Location: pnw iTrader: (0)	Would it be wise to occasionally trickle charge the two 12v batteries or is the ev charge of these batteries sufficient to keep them in good shape for 4-5 years? If so does anyone know if they are linked together so that the 12v charging connection in the engine compartment will charge both of them simultaneously? Also would they both be gel and need to be charged at low level? Thanks in advance for replies.
	Appreciate 0 Quote

06-05-2023, 11:39 PM	#11
jad03060 Major General 3206 Rep 6,872 Posts Drives: X5 45e Join Date: Aug 2018 Location: NH iTrader: (0)	They're AGM batteries, and if you use the battery charging points under the hood, yes, both batteries will be charged. There's still some questions about whether the HVB system, when the vehicle is off, charges the 12vdc batteries, but it does when you're charging them, or if you're driving, but BMW does not generally try to keep them at 100%. IMHO, an occasional use of a trickle charger is worthwhile. The area tech rep thought it did, but wasn't sure. He said he'd get back to me, but it's been over a week now, with no response. If the system was not being used over an extended period of time, without any charging being hooked up, people have reported the HVB retained their charge which, I think, would not be true if the parasitic losses in the 12vdc system required them to be recharged during that interval, and bring the HVB level down, at least some.
	Appreciate 0 Quote