[jad03060]

Since the 12vdc battery powers all of the 'normal' electronics in the vehicle, seat heaters, radio, rear window defroster, fans, wipers, lights, computers, etc., and those are required to actually 'start' up the vehicle to get it into READY state, you have a big brick if the 12vdc battery can't do its job. When 'off' modern vehicles are still running some functions:
- alarm
- comfort access (if present)
- cellular connection
- status monitoring
- even though most modules are in 'sleep' mode, they are 'on' enough so that they can be activated when you turn the vehicle on, or try to do something, like recognize hitting the start button, or even turning on the cabin lights when you open the door as those are controlled via the computer, not the door switch directly. There is some continuing load on the 12vdc battery. There is logic in the vehicle to shut down additional things over time if the 12vdc battery gets discharged to a certain level, but that even that will eventually discharge the 12vdc battery so nothing works.

On the 45e, the compressor for cooling is electrically driven as is all of the heating...there's no alternator.

The main batteries, when in READY state, run a DC-DC inverter that runs all of the 12vdc stuff, but the computers needed to enable it first need the 12vdc battery to power them...once it gets to READY, it can run them itself because of the DC-DC inverter while recharging the 12vdc battery in the process (assuming it will hold a charge). SO the key question is, is there enough 12vdc battery capacity to turn on the electronics so that the main batteries can then power things.

Like any battery, including the LiON ones, cold weather decreases their ability to supply voltage and current. This is much more of an issue with a lead-acid battery, even an AGM type, which most (if not all) BMWs use for their 12vdc batteries.

I think there's a 'transport' mode they use when shipping the vehicle that essentially disconnects more 12vdc loads, but that's not something the owner normally has access to. The user's manual doesn't list many precautions for storage, but there are a few things that are discussed.

If I were going to leave the vehicle unattended for extended times, I'd consider using a battery maintainer on the 12vdc battery, or maybe removing it entirely and maintaining it out of the vehicle. I do not know how long you can let the vehicle just sit with no use before you'll have problems with the 12vdc battery.

I do not know if the HV batteries, if an EVSE is plugged in, will also maintain the 12vdc battery. Some have said no, but on their pure EV model in the i3, it did keep the 12vdc battery charged if plugged in, so they've experienced that engineering task that could be applied to the 45e, but it doesn't happen if it's not plugged into an EVSE for sure that I can tell. Keep in mind, though, that the vehicle doesn't activate the EVSE until the main batteries charge level drops, and those, since there's not much happening, can take many days (likely weeks) before it might turn on to restore the charge, and if so, during that time, there likely isn't any DC-DC converter action to power the 12vdc battery.

Before I sold it, my ICE BMW wasn't driven much, and the 12vdc battery would die if it wasn't driven at least every couple of weeks in the winter, and, it would require it to be driven longer distances to bring the level back up to full. On many of the ICE BMWs, they've put the alternator on a clutch, so the load on the engine is less, and only engage the alternator under certain conditions, which can cycle the charge level on the 12vdc battery more. I found if I didn't use a battery maintainer on it, a battery wouldn't last more than a year or two and may have required a jump start to get it going. My 45e rarely gets driven daily, but usually at least once a week, and in the 15-months I've had it, haven't seen any issues or warnings about the 12vdc battery status.

[Walrusmode]

Thank you for the comprehensive information jad03060 !

I'm headed to the dealer for another issue in my car where I can't seem to stay and cycle thru the presets (keeps going to XM...) so I'll ask the mechanics about how the EV batteries, including while charging, impact the 12V battery. Maybe I'll get some new info to share.

[evodz]

Is it possible for the 12v battery to die and require a jump if you say, leave the radio running? I've been going to drive in movies and turn the car on about halfway through just to ensure it doesn't die on me

[jad03060]

Unless the battery was really low, and the fact that it turns itself off if you're not in the ready state after about 10-minutes or so (you can turn it back on for another cycle), it would be hard to have the radio drain the battery down too far. The computer will shut stuff down, and also issue a warning message before it gets down too low.

[speedfrk]

So living with the 45e as a PHEV in winter, using the climate control a lot is hard on the 12v system. If you run it down too much the ICE turns on without warning. I've had this in the summer too with lots of A/C. Due to the EME, it can charge ever so little back to the 12v. I know it's not much. If I want to go to pure electric (I'm usually in ECO Pro), it'll tone down all the HVAC to what the EME is able to support off the high voltage pack. At least I'm pretty sure that's what I see and why. Doing slow charges at 6A helps a lot but I still do the maintainer every couple of weeks. It needs the time to condition the 12v properly.

[DRMura]

Thanks to everyone for the great information in this thread. I ordered a 45e in April and it has just now been dispatched from the factory. I live in the northeast USA so it hopefully will be at the dealer shortly. Before I drive the car, I wanted to understand how the high voltage system works along with the 12v system, and this discussion and others have been very helpful. From what I gather, the 12v battery is there mainly to start up the electronics in the car, but once driven, the high voltage system powers the 12v electronics via a DC-to-DC converter. This is similar to an alternator running in a non-EV. Basically, all the electronics run off the 12v system, and the high voltage batteries are there to power the electric motor and provide charging to the 12v battery while the car is driven. I’ve ordered the car with all the options and all of them are included according to MyGarage. I was concerned that all the extra power consumption for the additional features would drain the 12v battery more quickly, but I guess there is nothing to worry about unless the car is not driven for an extended period.

[jad03060]

Originally Posted by nZtiZia

ok, so when the 45e is in electric mode (99% of the time for me), the HV system keeps the 12V battery charged via the DC/DC converter. when the 45e's ICE is running, the starter/generator spins and therefore keeps the 12V battery charged.

Nope...the starter motor is only used to start the ICE when you are stopped. When the vehicle is in motion and it needs to start the ICE, clutches in the transmission engage and the ICE is 'tow' started like popping the clutch on a manual transmissioned vehicle, powered by the EV motor and momentum.

When needed, like when the HVB is discharged, the ICE is running, it will turn the EV motor into a generator (using those same clutches), feeding the HVB, which feeds the DC-DC inverter keeping the 12vdc system operational.

As long as you have gas, once the vehicle is running, it will continue to run, feed the 12vdc system, which powers all of the computers, lights, fans, heaters, etc. Without enough 12vdc battery, you can't turn the computers on or power the starter motor, so you're dead in the water.

[meatball]

How swappable is this system? Can a lithium ion battery be put in instead? Also, what sort of burst and sustained discharge rates typically come from the AGM battery in the 45e system? Not sure if it's different than standard AGM.

I'd love to just let a small solar panel trickle charge my 12v battery to help reduce the drag on the HV battery.


Why? I have rampant ADHD and love to tinker

[viperdoc]

Originally Posted by jad03060

Nope...the starter motor is only used to start the ICE when you are stopped. When the vehicle is in motion and it needs to start the ICE, clutches in the transmission engage and the ICE is 'tow' started like popping the clutch on a manual transmissioned vehicle, powered by the EV motor and momentum.

When needed, like when the HVB is discharged, the ICE is running, it will turn the EV motor into a generator (using those same clutches), feeding the HVB, which feeds the DC-DC inverter keeping the 12vdc system operational.

As long as you have gas, once the vehicle is running, it will continue to run, feed the 12vdc system, which powers all of the computers, lights, fans, heaters, etc. Without enough 12vdc battery, you can't turn the computers on or power the starter motor, so you're dead in the water.

Thanks for this. I am hoping this is my issue. I just posted separately that my wife went to start our 45e and it just died completely. Currently at the dealer. Hopefully they'll say it was just the 12v. No power at all

[nZtiZia]

Originally Posted by viperdoc

Thanks for this. I am hoping this is my issue. I just posted separately that my wife went to start our 45e and it just died completely. Currently at the dealer. Hopefully they'll say it was just the 12v. No power at all

keep us posted. i'm 14k miles on my 2021 45e (delivered Dec 2020) so this is concerning to me

[BillW2]

My late MY 2021 545E is broken down in MI. 12 Volt system is dead. There are 2 12 volt batteries in mine. A very large 950 CCA battery and a compact 575 CCA battery. The big one is so dead that it will not even power my battery tester. Had to have it towed to a dealer an hour away last evening. I was planning on driving 750 miles to NC today. Very disappointed a 2 year old car has left me stranded out of town for an unknown duration. The dealer has now had the car for 3/4 of a day and still hasn't figured out why it is dead. I did jump it and it would only run while connected to the jumper battery. My guess is that the big battery is so bad it can't even allow 12 volts to pass through it. Time will tell. I loved my X5 till now but this is so frustrating I might have to trade back to a Cayenne.

[jad03060]

BMW's 12vdc battery control logic does not try to keep them fully charged...it will let them get down to about 70%. On their ICE versions, the alternator is on a clutch, and only engages to charge the batteries during deceleration or when you're actually applying the brakes, unless it drops below that 70% (one reason why they tend to use large AGM batteries). THe PHEV is similar...when regeneration is available, it uses that excess to put back into the HVB, but the 12vdc system isn't prioritized...now, since the 12vdc bus needs to be operating, those batteries will get charged, but there's not a huge excess of 12vdc power. That's one reason why the owner's manual says that you can be jumpstarted if required, you CANNOT reliably or safely jump start someone else's vehicle with your PHEV...there just isn't a huge excess of 12vdc power that a dead vehicle needs, especially if it's cold out.

So, IMHO, it's not a bad idea to put a battery maintainer on ANY BMW at least periodically. If you do, your battery will last longer. On my first ICE BMW, the first battery lasted a year before the dealer replaced it...I started to use a battery maintainer on it and that one lasted 7-years...way beyond 'normal' lifespan, especially on a BMW.

[streborx]

I've often wondered about the portable jump chargers such as Noco's GB series and their utility. If you have a marginal starter battery, why not buy a new one rather than toting around one of these jump chargers? The experiences and info in this post certainly justify having one if you own an e-series vehicle of any brand. I'm not going to own a hybrid, but I wouldn't driving around without a jump charger if I did own one.

[meatball]

Originally Posted by BillW2

My late MY 2021 545E is broken down in MI. 12 Volt system is dead. There are 2 12 volt batteries in mine. A very large 950 CCA battery and a compact 575 CCA battery. The big one is so dead that it will not even power my battery tester. Had to have it towed to a dealer an hour away last evening. I was planning on driving 750 miles to NC today. Very disappointed a 2 year old car has left me stranded out of town for an unknown duration. The dealer has now had the car for 3/4 of a day and still hasn't figured out why it is dead. I did jump it and it would only run while connected to the jumper battery. My guess is that the big battery is so bad it can't even allow 12 volts to pass through it. Time will tell. I loved my X5 till now but this is so frustrating I might have to trade back to a Cayenne.

Anyone know which of these two batteries powers the 12v systems vs the starter? Im thinking the larger one powers all the 12v stuff, but not sure.

[streborx]

Originally Posted by meatball

Anyone know which of these two batteries powers the 12v systems vs the starter? Im thinking the larger one powers all the 12v stuff, but not sure.

My X7 is comparably configured -- 2 batteries, one under the floor in the boot and the other under the hood in front of the passenger seat. As far as I know, it's the boot battery that's the workhorse. It powers the starter and most of the lighting and accessories. The smaller battery is (I think) used for the dynamic handling package features.

As others have noted, the big battery is never fully charged by the car's alternator, and can deplete in a couple weeks, perhaps sooner as it ages. Batteries can be finicky, and although you should get a solid 3 years out of one (more usually), there are always exceptions. Manufacturing defects can lead to premature failure.

The dealer should be able to connect test equipment to determine if there is some abnormal current consumption from an electrical component defect. But if no defect can be found, install a new battery and hope the problem was only the old battery. If you leave the car parked for more than 2 weeks, put a battery tender on the jump start terminals under the hood.

[BillW2]

Update to my original post. It only got worse. This is what I sent to the dealer that charged me $170 to charge the bad battery instead of replacing the battery under warranty as it should have:
"On September 27, 2023 I had my two year old X545E towed in to your dealership. The battery was dead. I told Jonah and at least one other service adviser that I was almost certain the battery was bad. I also told them I was planning on hauling my new boat from MI to NC as soon as the car was ready to go.
After keeping the car nearly all day, I was told that it was caused by the guys who hooked up my boat leaving the lights on and that all is well. See RO # 6061830/1.
Well, the next day, I was stranded in the Virgina mountains at my second fuel stop. The car was completely dead for the 3rd time in 4 days. It was the battery just like I thought. BMW roadside assistance couldn’t find anyone to help me. Fortunately, I found an auto repair shop that had a battery close enough to get me going again and they came to the gas station and changed it out for me. Cost: $346.48
Given that the factory battery died 3 times in 4 days including twice after having been driven for over 6 hours immediately before being dead in only a few minutes, I do not believe that the battery could have passed testing if your mechanic had bothered to take the time to actually run a test on the battery. I actually had a tester in my car but the battery was to dead to even run a test. In fact, it was so dead that I had to jump the car to open the back hatch to get to the battery.
I request a refund for the $170 plus surcharges and tax your dealership charged for charging the bad battery. Who do I need to contact about getting reimbursed for the $350 I had pay for my new battery that should have been replaced by your dealership under warranty?"

The dealer called, apologized and said they would send me the $170.00. Even after replacing the battery with an aftermarket my nav system would not work so I took it to a BMW dealer in NC. They cleared the low voltage faults in the system and claim that has fixed the problem. Even though I had an appointment, they still took two days to look at the car and a total of three days to get it back to me including changing tires. They couldn't replace the battery under warranty since I didn't keep the bad BMW battery that only lasted 27 months. URG!