Master thread: Model 3 12v Battery issues, monitoring, Aftermarket replacement

[cyberjoe]

Is the 12V required to drive the car if you can get in it?

-Don- Reno, NV

The car is completely DEAD. you cannot get inside the car, you cannot open the door or trunk. Could be dangerous situation in the winter and if babies/toddlers inside the car when the car battery dies.

 

[DonTom]

The car is completely DEAD. you cannot get inside the car, you cannot open the door or trunk. Could be dangerous situation in the winter and if babies/toddlers inside the car when the car battery dies.

I realize we cannot get in the car as the locks are 12 volts. But I was wondering what would happen if we could. Seems to me if we can get the car on, the DC2DC converter will supply the 12 volts. But is the 12V also required to get the car turned on?

-Don- Reno

 

[rrolsbe]

If the 12V is dead, you use the 9V battery to open the frunk. Then remove the cable from the negative 12V battery terminal using a 10MM wrench. Then either swap in your good spare battery or connect your jumpstarter between the positive post and the removed negative cable. You could connect the jumpstarter without removing the negative side but if the failed battery has developed a short you would have a problem. When power is connected to the battery cables, the HV contactors will close allowing you access to the car and it can then be driven. The 12V battery is only needed to close the contactors and run the 12V accessories while the car is in the sleep state. I recommend watching the battery swap out video someone listed above. You would not need to lift the connector under the back seat because the contactors would already be open due to the failed 12V battery. Also, if you do not understand what/why you are doing the steps outline above, contact Tesla Roadside service.

 

[elptxjc]

I heard somewhere that all it takes is a little 9 volt battery

I didn't know that, so learned something important today. However, I saw under my car, and there's nothing. The only round part is the one for the tow hook... but I couldn't remove it. Can somebody please post a picture of the '9-V' battery cover? And how to remove it, exactly? Thank you.

I plan on replacing it myself. A lot less hassle. I usually fix my own problems even during the warranty period at my own cost

Me too, and will probably replace the battery pro-actively with a Tesla one (since it's the cheapest). Having said that, your linked video doesn't mention anything about removing the connector under the rear right seat. It'd be dangerous to remove the battery as shown on that video if it has even a little current, so I'd always remove the seat connector before removing the + post. I need to re-check the procedure, but I remember it was remove '-' cable, remove rear seat connector, then remove '+' battery terminal, and replace battery.

If the 12V is dead, you use the 9V battery to open the frunk. Then remove the cable from the negative 12V battery terminal using a 10MM wrench. Then either swap in your good spare battery or connect your jumpstarter between the positive post and the removed negative cable.

Thank you for that important information. So I guess it's important to also have one of those Li-Ion small jump-starter battery packs, to re-start the car, and get to your destination. The only thing we'd have to put somewhere is a '9V' battery. I'll take care of doing all of that soon, but need to learn where exactly is the 9V plug, and how it's removed. Thank you.

EDIT: Looked at a video on Youtube, and the wires are behind the tow-hook plug. I had a hard time removing it for the first time, but could do it without damage. The hook is at the 1:30pm position (where you need to push), and the clip at the 7:30pm position, which is where you need to stick a plastic trim tool to pop out the cover. In my car, the '-' wire was attached to the cover, rather than the '+', but checked voltage after waking up the car, and there's no voltage, so no risk of a short. Will try to fit a 9V battery in the hole there (with terminals taped up), and see if I can close the cover; it'd be the perfect solution. By the way, read that if the car is locked, you CANNOT open the frunk like that, so that'd be a problem if true.

 

[rrolsbe]

I didn't know that, so learned something important today. However, I saw under my car, and there's nothing. The only round part is the one for the tow hook... but I couldn't remove it. Can somebody please post a picture of the '9-V' battery cover? And how to remove it, exactly? Thank you.


Me too, and will probably replace the battery pro-actively with a Tesla one (since it's the cheapest). Having said that, your linked video doesn't mention anything about removing the connector under the rear right seat. It'd be dangerous to remove the battery as shown on that video if it has even a little current, so I'd always remove the seat connector before removing the + post. I need to re-check the procedure, but I remember it was remove '-' cable, remove rear seat connector, then remove '+' battery terminal, and replace battery.


Thank you for that important information. So I guess it's important to also have one of those Li-Ion small jump-starter battery packs, to re-start the car, and get to your destination. The only thing we'd have to put somewhere is a '9V' battery. I'll take care of doing all of that soon, but need to learn where exactly is the 9V plug, and how it's removed. Thank you.

It is not a 9V plug it is two wires located behind the front tow hook cover. The car users manual shows using a 12V battery but user have found out a brand new 9V battery works.

The are several videos on Youtube showing how to open the frunk using a 9 volt battery, I recommend watching some of them. The tow hook cover can be hard to remove as can retrieving the wires. Watch the video(s) and try it for yourself before you are in a pinch.

 

[DonTom]

I didn't know that, so learned something important today. However, I saw under my car, and there's nothing. The only round part is the one for the tow hook... but I couldn't remove it. Can somebody please post a picture of the '9-V' battery cover? And how to remove it, exactly? Thank you.

It's the front of the car, not under:

 

[DonTom]

That was the first time I removed that cap. I am glad I did, because I cannot figure how to use it. There is only a single wire. How is that going to work? What do we used for the return path or ground with our 9 V battery?

Edit: Disregard. See posts below.

-Don- Reno, NV

 

[DonTom]

 

[DonTom]

I didn't quite understand that. What do we do it the 12 volt battery is 100% dead and we cannot use the phone to unlock it????? And if we can unlock the doors, why do we need to use the 9 volt battery to unlock the Frunk?

EDIT:I just now watched it again. I now see the 9V will work when the 12 battery is dead, but not now work when the 12 Volt battery is good (unless the car is unlocked anyway).

Also, I couldn't find the positive wire in my hole. I will look again now that I know that it should be in there somewhere.

Edit: I Just found the positive wire, it Ys with the wire on the cap 4.5 inches from the wire on the cap. It was stuck in there very tight.

I had no trouble removing the cap with a straight slot screwdriver from around 7 or 8 o'clock on the cap.


-Don- Reno, NV

 

[DonTom]

I just now used my FOB to unlock my Tesla M3 and used the 9V battery to open the Frunk. Worked perfectly. So then I locked the doors with my FOB and tried the 9V battery again and it did NOT work, just as as it shouldn't,

I guess the only way we can do a real test is either wait for the 12V battery to go dead or disconnect (using the correct procedure to to turn off the car--Safety & Security--Power Off). I will just assume it will really work when the 12 V battery really goes dead, regardless if the car is locked or not.

BTW, I just discovered turning the car "off" does NOT disable the 12VDC. I could still use the auto windows and FOB with the car turned off. But only the brake pedal turns the screen and car back on.

IMO, everybody who owns a Tesla M3 should try a 9V battery to open the Frunk to be sure they can when the battery really goes dead. Car has to be unlocked (unless your 12V Battery is dead!).

-Don- Reno, NV

 

[elptxjc]

Okay gang, went to the garage and popped the plug; it was a PITA the first time. I did it THREE times, to loosen the plastic a little bit, and now I can open it without any tools, which is the goal. In addition, I wanted a solution to the 9V battery issue, and this is what I did (pics below): I shoved a brand new battery (with the posts double-taped) in there, positioned so I can push on the 1:30pm position, cut off the part of the cover plug where one wire was attached (which is not needed IMO. Plus if somebody is going to steal it, prefer the thief to take it easily, rather than pull on those wires), and taped the 2 wires together, separated with tape, although there's no voltage on them. Now, I don't need to remember carrying a 9V battery . And it's good to know we can open the frunk with it even if car is locked with a dead battery.

Finally, to 'start' the car, we still need a 'jumper' battery, correct? So will buy one of those light portable packs I have on my ICE car ($100), and a 10mm wrench, and permanently leave them in the frunk, to be able to drive off if the 12V battery craps out.

 

[elptxjc]

Hey gang, the edit time elapsed, so need to start a new post. My wife asked how exactly to 'start' the car, and I didn't have an answer. By the way, I added a yellow zip-tie to the cables, to fish them out easily, in case they hide, since I removed the part where one of them plug to the cap. Super easy to open now, and I have the battery there, so no worries anymore.

After you open the frunk, I have the following questions:
1. It should be 99.99% safe to just jump the battery like an ICE car, without the need to remove negative cable, no? But is it best to attach negative to the battery itself, or to a chassis ground, like on an ICE car? And yes, always attach positive terminal first, then negative (either to ground, like on ICE cars, or battery terminal, depending what the experts say). Or is the negative terminal absolutely has to be removed, and attach the jumper terminal there? Then turn on battery pack as a jumper.
2. After car is energized, and you open the door, what's next? Can you remove the jumper pack at that point? Or do you need to actually put the car in D, before removing jumper device? Please provide details. Thank you .

 

[rrolsbe]

In most cases using a Jumpstarter/jumping from another vehicle ,without lifting the negative cable, would probably work and be safe; however, not knowing why the 12V died, i like to error on the side of caution. After the contactors close ,I would wait a couple of minutes before removing Jumpstarter or jumper cables. I am pretty sure you would only need to wait until you hear the pumps start after the contactors close, which is just a few seconds? What needs to be operational is the DC-to-DC converter to supply 12V power. When I disconnected the negative cable after the car transitioned out of sleep state, the car was drive-able and seemed to be fully functional. I did get an onscreen error that the 12V battery was disconnected (which was true). After returning home, I would charge and analyze what happen to the 12V battery before reconnecting it to the car.

 

[DonTom]

Hey gang, the edit time elapsed, so need to start a new post. My wife asked how exactly to 'start' the car, and I didn't have an answer. By the way, I added a yellow zip-tie to the cables, to fish them out easily, in case they hide, since I removed the part where one of them plug to the cap. Super easy to open now, and I have the battery there, so no worries anymore.

After you open the frunk, I have the following questions:
1. It should be 99.99% safe to just jump the battery like an ICE car, without the need to remove negative cable, no? But is it best to attach negative to the battery itself, or to a chassis ground, like on an ICE car? And yes, always attach positive terminal first, then negative (either to ground, like on ICE cars, or battery terminal, depending what the experts say). Or is the negative terminal absolutely has to be removed, and attach the jumper terminal there? Then turn on battery pack as a jumper.
2. After car is energized, and you open the door, what's next? Can you remove the jumper pack at that point? Or do you need to actually put the car in D, before removing jumper device? Please provide details. Thank you .

I wonder if the Tesla even uses the chassis ground for the 12 volts. I can tell you that my Zero motorcycles uses a floating ground. The bikes doesn't use the frame to complete any electrical circuits. So to even measure any voltages, I use the headlamp low in place of a frame ground.

In EV cars, I don't think they ever use the frame for the HV stuff as that could be very dangerous if they need to use metal tools to pry open a car after a serious accident with people still in it. You don't want a ground to be able to short tools to, if the hot is accidentally contacted with a metal tool. . But I do not know about the 12 Volts. When I change my battery I will check to see if the negative side is going to the frame. But I would NOT use the frame in an EV if I didn't know for sure that it went to the battery negative. And while it could even be positive ground for 12 VDC, I would expect it to use no frame ground at all. And I would assume such in an EV if I didn't know, since that is the way even my electric motorcycles are.

After you once have the car on, I assume the DC2DC will keep the 12 volts on regardless of the battery. I don't know when the DC2DC comes on, but it is on for sure when you're ready to drive. Perhaps I can test for that also, when I change my 12 V Tesla battery. I will then report back here.

-Don- Reno, NV

 

[elptxjc]

Perhaps I can test for that also, when I change my 12 V Tesla battery. I will then report back here.

Awesome! Thanks Don . Just to know at which point the car is energized, and we can remove the jumper device.

And I fully agree with your assessment of chassis ground; makes a lot of sense. But out of curiosity, please see if you can trace the 12V negative battery terminal. So the only question left is if we jump the battery with the negative cable connected or not. My take is there's no need to remove it, and here's why. Let's assume the 12V battery had a short; it'd have damaged the car already, no? But if it didn't damage it, it shouldn't damage it when just jumping it to energize the contactors, no? The worst that could happen is that the contactors are not closed, so at that point, we'd have to proceed to remove the negative cable, no? By the way, it's extremely rare to see a full short of a 12V battery. If anything, maybe one cell or two, but the battery still has power. Not having to remove the negative cable would simplify jumping the car a lot, especially for women. Or guys not mechanically inclined .

EDIT: Hey Don, can you please tell me if you can engage all clips after you reinstall the battery cover? I couldn't engage the ones next to the frunk rubber seal. None of them. I could hear them wanting to engage, but pop back out. If I press any harder, I'd break something. The whole thing feels extremely flimsy. Just want to know if my car is the only one. The cover is safely in place, since the side and top ones did engage. Maybe something changed for 2021? Oh, and had 1 clip missing; need to ask Tesla for one. Thank you.

 

[DonTom]

Just to know at which point the car is energized, and we can remove the jumper device.

My "jumper device" do you mean a small battery pack in parallel with the dead 12 V battery?

Let's assume the 12V battery had a short; it'd have damaged the car already, no?

Hard to say what will happen when the DC2DC converter is shorted. It depends on the design. Some could just turn off automatically, if they have current limiting, which is not uncommon these days, but I would not bet on it either.

-Don- Reno, NV

 

[elptxjc]

By "jumper device" do you mean a small battery pack in parallel with the dead 12 V battery?

Yeah, I have exactly this one: https://www.amazon.com/gp/product/B015TKUPIC/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1 . Much safer than using a second battery and jumper cables. If you reverse the cables, nothing happens. And I'm 99.99% sure that our DC2DC converter has the same 'short' protection, hence not having to remove the negative battery cable. I'd like to ask that to a Tesla factory tech guy, so we know for sure if it'd be safe or not to 'jump' the dead battery still connected.

 

[elptxjc]

Hey guys, I need to buy a 'booster pack' for the Tesla; the one I linked above is for my large 12.1:1 CR 32V V8 car, which needs a lot of juice. For the Tesla, a much smaller one would suffice, right? A link for a proven one for this task would be great. Mine is heavy, so something lighter would be better. Thank you.

 

[jmbloom_m3p]

There is a whole thread on this issue. There are plastic supports under that trim piece that break really easily. Totally a fail on design by Tesla. There are 3D printed parts that fix it and work amazingly well. I do not have a 3D printer so I used an online service to print mine. Worked great. Here is a video of the fix —

And the thingiverse part model

Model 3 frunk reinforcement part by joanquro

EDIT: Hey Don, can you please tell me if you can engage all clips after you reinstall the battery cover? I couldn't engage the ones next to the frunk rubber seal. None of them. I could hear them wanting to engage, but pop back out. If I press any harder, I'd break something. The whole thing feels extremely flimsy. Just want to know if my car is the only one. The cover is safely in place, since the side and top ones did engage. Maybe something changed for 2021? Oh, and had 1 clip missing; need to ask Tesla for one. Thank you.

 

[DonTom]

I would guess that it is even safer to leave the old battery connected. Even if it has a shorted cell in the old battery, it most likely won't be a dead short and the voltage will still come up to the voltage of your GB40 when properly connected. But it is somewhat of guesswork, as batteries can fail in different ways.

Another guess I have is the DC2DC converter is activated as soon as the car is ready to drive. Perhaps a foot on the brake pedal or putting the car in gear.

I received my new 13 volt lithium battery today, but I don't have an error message or any problem yet with my stock 12 VDC battery. I have the new battery in the Frunk along with a 10 MM open end wrench. I have not yet decided if I should replace the battery with the new one or just wait until there is an indication that I have a bad 12V battery.

But even if I do NOT replace it, within a few days I will do some testing with the 12V battery just to find out when the DC2DC comes on and to see if the neg side uses the frame ground, if there is a frame ground in there that I can get to.

I have a few other projects to work on first.

-Don- Auburn, CA