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So I was checking out under the hood yesterday and I saw a 12v battery hidden away and was like hu what is that for... Seems strange on an electric car that is mostly all battery. Anyway this is a good read if you dont all ready know.
 

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So I was checking out under the hood yesterday and I saw a 12v battery hidden away and was like hu what is that for... Seems strange on an electric car that is mostly all battery. Anyway this is a good read if you dont all ready know.
Yep... one of the biggest things is opening/closing the contacts for the HV (main) battery. On a Tesla (as I have first hand experience), if the 12V battery dies, and your car is fully asleep, it will not come back on without the 12V battery, even if it has plenty of charge, and I assume it's the same in the i4. This has left plenty of people stranded, especially because the Tesla 12v is in the frunk, which is only accessible via a button on the screen, which isn't available when the 12v is dead. The backup method is to use a 9v battery to pop the frunk using the cutout in the front where the towing bolt goes.

So that brings up a good question on the i4... is the hood release manual? (In other words, does it need the 12v to be available to open the hood, to access the battery.
 
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Discussion Starter · #3 ·
Yep... one of the biggest things is opening/closing the contacts for the HV (main) battery. On a Tesla (as I have first hand experience), if the 12V battery dies, and your car is fully asleep, it will not come back on without the 12V battery, even if it has plenty of charge, and I assume it's the same in the i4. This has left plenty of people stranded, especially because the Tesla 12v is in the frunk, which is only accessible via a button on the screen, which isn't available when the 12v is dead. The backup method is to use a 9v battery to pop the frunk using the cutout in the front where the towing bolt goes.

So that brings up a good question on the i4... is the hood release manual? (In other words, does it need the 12v to be available to open the hood, to access the battery.
yes the i4 hood is manual its a double pull handle under the dash just like a normal car
 

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yes the i4 hood is manual its a double pull handle under the dash just like a normal car
That's 'cause BMW has been building cars for a long time. (Tesla, not so much.) Even with the 12V dead, you can still access the interior (and the hood control) using the integrated key. The key slot is not visible, but is accessed by lifting the door handle. There are a lot of functional and emergency details in design that come with experience. It's why I'm reluctant to go with the "new" car companies - they may have interesting (and sometimes quirky) technology but they lack experience in car design and building.
 

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Yep... one of the biggest things is opening/closing the contacts for the HV (main) battery. On a Tesla (as I have first hand experience), if the 12V battery dies, and your car is fully asleep, it will not come back on without the 12V battery, even if it has plenty of charge, and I assume it's the same in the i4. This has left plenty of people stranded, especially because the Tesla 12v is in the frunk, which is only accessible via a button on the screen, which isn't available when the 12v is dead. The backup method is to use a 9v battery to pop the frunk using the cutout in the front where the towing bolt goes.

So that brings up a good question on the i4... is the hood release manual? (In other words, does it need the 12v to be available to open the hood, to access the battery.
So do you have to condition the 12v battery like on a ICE car in storage?
 

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Maybe a totally naive question since I’m new to EVs but would it be safe to keep a 12v on hand in the event it dies?
IMHO, no more than you would if it was an ICE car. Yes, if the 12v fails completely, it won't start - just like an ICE car. With your key and the manual trunk latch, in the BMW, you can still lift the hood to access the 12V supply. Teslas are a different breed and access may be different. I believe @linerjoe explained his method earlier in this thread.
 

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IMHO, no more than you would if it was an ICE car. Yes, if the 12v fails completely, it won't start - just like an ICE car. With your key and the manual trunk latch, in the BMW, you can still lift the hood to access the 12V supply. Teslas are a different breed and access may be different. I believe @linerjoe explained his method earlier in this thread.
In my Icemobile I carry a lithium battery jumper system. It weighs a few pounds and has a capacity of 18Amp-hours at 12v.

we don't have a starter in the i4, but we can connect such a battery and leave it for a while to transfer charge which could charge the 12 volt battery by a third of capacity.

And just for fun, once you get your i4 started, you may be able to recharge the jumper battery from the 12 volt socket in your trunk.
 

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In my Icemobile I carry a lithium battery jumper system. It weighs a few pounds and has a capacity of 18Amp-hours at 12v.

we don't have a starter in the i4, but we can connect such a battery and leave it for a while to transfer charge which could charge the 12 volt battery by a third of capacity.

And just for fun, once you get your i4 started, you may be able to recharge the jumper battery from the 12 volt socket in your trunk.
I've got one of those small emergency cranking batteries, but keep forgetting to charge it ;)

I'm guessing, in theory anyway, you could energise the 12V system by back-feeding any 12v socket in the car. You don't have to "crank" the car, just get enough current to fire up the electronics and HV relay. Once the electronics are energised, the main battery would again be able to charge the 12v - if it's capable of taking a charge. Kind of depends on how it failed. Just guessing here.
 

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I've got one of those small emergency cranking batteries, but keep forgetting to charge it ;)

I'm guessing, in theory anyway, you could energise the 12V system by back-feeding any 12v socket in the car. You don't have to "crank" the car, just get enough current to fire up the electronics and HV relay. Once the electronics are energised, the main battery would again be able to charge the 12v - if it's capable of taking a charge. Kind of depends on how it failed. Just guessing here.
That could be even easier than my idea. You just carry 6-8 feet of cable.

one issue could be the amperage. The jumper battery gives some 18 amps, while the 12 volt socket only 1/2
That could be even easier than my idea. You just carry 6-8 feet of cable.

one issue could be the amperage. The jumper battery gives some 18 amps, while the 12 volt socket on the console may give only 1/2 - 1 amp
looks like I am wrong. The socket may do 10-20 amps
 

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I, too, am interested in this topic. I have long known about the 12V in EVs, but every car is different. I have had my i4 M50 for only a week, and I'm already thinking about what could go wrong.

Does anyone know how exactly the 12V gets charged? Is it the actual voltage from the main battery pack, or is it the motion the wheels themselves as you drive it?

Certainly, a 12V battery that won't take a charge means you're hosed. You need a new one. Fortunately, they're often available in Anytown, USA.

But what about, say, sitting, parked with the main battery fully charged, in a parking lot with all the interior and exterior lights on, listening to music and maybe charging my phone? With a 1 year old 12V battery, how long might I have before I need a jumpstart? It's not like it needs to push a starter crank arm, just basically needs to turn on all the other components for Drive mode. But does the 12V start charging then, or when you actually move?

These are the things I have been thinking about lately.
 

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The regen braking recharges the traction battery, not the 12V. The 12V can take charge from the traction battery whether or not the car is in motion.
 

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The regen braking recharges the traction battery, not the 12V. The 12V can take charge from the traction battery whether or not the car is in motion.
But only when the car is in "drive ready state?"
 

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can someone post a pic of where the 12 volt battery is on the i4? pretty please. Thinking about getting one of those small lithium jumpers. Was going to for the other car, may as well get two, lol
 
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But what about, say, sitting, parked with the main battery fully charged, in a parking lot with all the interior and exterior lights on, listening to music and maybe charging my phone? With a 1 year old 12V battery, how long might I have before I need a jumpstart? It's not like it needs to push a starter crank arm, just basically needs to turn on all the other components for Drive mode. But does the 12V start charging then, or when you actually move?

These are the things I have been thinking about lately.
I can't speak for the i4, but in a Tesla, sitting there listening to music, running HVAC, etc, comes from the high voltage battery. Unless the car is in deep sleep, you're using the high voltage battery, basically. So if a door is open, if you've pressed the brake to "wake the car", etc.

I'm guessing it's similar in the i4 (if the "on" button is pushed)?
 

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Thoughts on a trickle charger if the car is going to be parked for awhile?
 
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The regen braking recharges the traction battery, not the 12V. The 12V can take charge from the traction battery whether or not the car is in motion.
This is what I would have thought, but wasn't entirely sure.

So, in my scenario, sitting idle, but in "drive ready mode," with the seat heaters, internal heat, and steering wheel heaters on, blasting the stereo, I'd expect to slowly deplete the "traction" (high-voltage) battery, and not have the 12v completely discharge and suddenly be unable to move the car forward. Assuming the traction battery is charged, and the 12V isn't defective, this is the right expectation, right?

Also, +1 on @Elle BMW 's request for a pointer to where the 12V actually is would help. I've never opened the hood on my i4, but I have had enough 12V's go bad in ICE cars to know it's best to be ready to change them. I just changed the one in my 4Runner in September.

Thanks.
 
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12v Battery location @Elle BMW and others. Its located under a small cover. Passenger side of the hood.
Hood Grille Automotive tire Automotive lighting Motor vehicle
 
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Both my Tesla (3 years old) and my wife's Tesla (2 years old) had their 12 v's die within a month of each other. Both times a warning message came up on the display and our app automatically made a service appointment where a Tesla mobile service person came to our home and replaced the battery. Say what you want about Tesla service but that was pretty cool.
 
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