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"Proactive" 12v battery replacement - good idea or overkill?

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View attachment 768092

Well, I jinxed it. Battery is original, so I guess 4 years isn't so bad given what people on here have been saying.

View attachment 768093

That a402 error seems new(ish). Either I got lucky and the battery fully died while the DC-DC was connected or Tesla is getting more proactive about checking while the car is in a powered state to try and reduce the number of people stranded.

Anyone know if I'll have trouble clearing these codes on my own if I replace the 12V while the DC-DC is on? Normally the processes is to wait for the car to sleep before swapping the battery, but I don't think that will ever happen with the a402 code present.
disconnect the old 12V battery, then disconnect the HV harness underneath the rear passenger seat. The car will disconnect the HV and it's safe to replace the battery.
Then re-connect the HV harness, then reconnect the NEW 12V battery.

All should be right with the world.
Might take a drive cycle to remove the errors.
 
disconnect the old 12V battery, then disconnect the HV harness underneath the rear passenger seat. The car will disconnect the HV and it's safe to replace the battery.
Then re-connect the HV harness, then reconnect the NEW 12V battery.

All should be right with the world.
Might take a drive cycle to remove the errors.
ALWAYS remove the negative terminal first and replace it last.
 
View attachment 768092

Well, I jinxed it. Battery is original, so I guess 4 years isn't so bad given what people on here have been saying.

View attachment 768093

That a402 error seems new(ish). Either I got lucky and the battery fully died while the DC-DC was connected or Tesla is getting more proactive about checking while the car is in a powered state to try and reduce the number of people stranded.

Anyone know if I'll have trouble clearing these codes on my own if I replace the 12V while the DC-DC is on? Normally the processes is to wait for the car to sleep before swapping the battery, but I don't think that will ever happen with the a402 code present.
Follow instructions in the Ohmmu site. The process is the same and it is illustrated on disconnecting the HV battery. the Atlas BX battery isn't available retail unless purchase over the counter at a Tesla Service Center. Mobile service can also come out and do the change. Or you can buy a 51R battery. Some have used AGM batteries with no messages. The factory battery is NOT AGM sen though many publications mistakenly say it is.
 
Well my local Tesla service center is closed Saturdays now apparently. I’m going out of town tomorrow, fingers crossed the car doesn’t leave me stranded I guess. Going to enable sentry mode as an extra effort to try and keep the car from sleeping.
Any autocrats store with a 51R battery should work or wait until Tesla opens. If they are back ordered go to local auto parts store.
 
Since I was out at the service center, I checked to see if there was any more info on the errors present.

a182
12V battery needs to be replaced
Set: The battery voltage is below 10.5V for 5 seconds or the 12V battery has been overcharged 10 times or the battery voltage reached 12.2V before the Ah count reached -2.25Ah 10 times or 4 voltage drops were observed when load current on 12V was greater than 20A.
Clear: The vehicle lost power from the 1wV battery and PCS (as would happen during 12V battery replacement).
Impact: The battery may lack the power to support vehicle 12V aux systems: car may fail to start and potentially high range loss will be experienced.

a402
Electrical system backup power is unavailable. Vehicle will consume more energy while idle.
Set: 12V battery is heavily degraded, disconnected, or reverse battery e-fuse is faulted
Clear: 12V battery is replaced, battery is re-connected, or reverse battery e-fuse fault clears
Impact: 12V battery is unable to support the vehicle and contactors will be permanently closed.

Nothing there that I didn't already know/assume, but the exact 12V fault conditions are interesting. Keeping the DC-DC always on (a402) seems to be working without issues. Aside from the car not sleeping I haven't noticed anything out of the ordinary.
 
Update: first major issue with 12V battery disconnected mode. There seems to be no battery heating whatsoever. Could't get the car to charge even after a few hours after cold-soaking overnight. Did some yo-yo driving around the block and now it's pulling a few kW. Haven't tried supercharging yet, but I have a feeling speeds will be pretty limited. I suspect the car is worried about coolant pump and/or radiator fan pulling too much power on the 12V bus. 12V accessory outlets and USB ports also seem to be disabled. But apparently I have enough power to keep the subwoofer enabled, weird choice haha.
 
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Update: first major issue with 12V battery disconnected mode. There seems to be no battery heating whatsoever. Could't get the car to charge even after a few hours after cold-soaking overnight. Did some yo-yo driving around the block and now it's pulling a few kW. Haven't tried supercharging yet, but I have a feeling speeds will be pretty limited. I suspect the car is worried about coolant pump and/or radiator fan pulling too much power on the 12V bus. 12V accessory outlets and USB ports also seem to be disabled. But apparently I have enough power to keep the subwoofer enabled, weird choice haha.
Sounds like you need to replace the 12 volt. A typical high quality 12 volt lead acid BCI group 51R will work. All you need is a 10mm socket. Takes about 15 minutes. The 12 volt is not heated. The procedure is best explained on the Ohmmu site. It involves opening doors and windows, opening Frunk, powering off car on safe menu, disconnecting the negative terminal, disconnecting the HV plug under the right rear seat. You must also remove the cover over the battery and the intake to the AC all with plastic buttons. Sounds co implicated but it isn't.
 
Sounds like you need to replace the 12 volt. A typical high quality 12 volt lead acid BCI group 51R will work. All you need is a 10mm socket. Takes about 15 minutes. The 12 volt is not heated. The procedure is best explained on the Ohmmu site. It involves opening doors and windows, opening Frunk, powering off car on safe menu, disconnecting the negative terminal, disconnecting the HV plug under the right rear seat. You must also remove the cover over the battery and the intake to the AC all with plastic buttons. Sounds co implicated but it isn't.
Oh I know the 12v needs to be replaced. I’m planning on buying the OE one from Tesla but they are closed on weekends apparently and I need my car.

Battery heating is referring to the high voltage pack. In this 12v battery disconnected mode (a402 fault) the car seems to disable heating of the high voltage pack, making charging in 20 degree temps difficult.

The odd behavior isn’t anything catastrophic for me but I figure it’s worth documenting so that people know what to expect if their 12v dies while away from home. Helpful info to decide whether preventative replacement is worth it (bringing things back to the subject of this thread haha)
 
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Since I was out at the service center, I checked to see if there was any more info on the errors present.

a182
12V battery needs to be replaced
Set: The battery voltage is below 10.5V for 5 seconds or the 12V battery has been overcharged 10 times or the battery voltage reached 12.2V before the Ah count reached -2.25Ah 10 times or 4 voltage drops were observed when load current on 12V was greater than 20A.
Clear: The vehicle lost power from the 1wV battery and PCS (as would happen during 12V battery replacement).
Impact: The battery may lack the power to support vehicle 12V aux systems: car may fail to start and potentially high range loss will be experienced.

a402
Electrical system backup power is unavailable. Vehicle will consume more energy while idle.
Set: 12V battery is heavily degraded, disconnected, or reverse battery e-fuse is faulted
Clear: 12V battery is replaced, battery is re-connected, or reverse battery e-fuse fault clears
Impact: 12V battery is unable to support the vehicle and contactors will be permanently closed.

Nothing there that I didn't already know/assume, but the exact 12V fault conditions are interesting. Keeping the DC-DC always on (a402) seems to be working without issues. Aside from the car not sleeping I haven't noticed anything out of the ordinary.
Question - The 12 V battery has been overcharged 10 times - what is overcharged. I wonder if there is a value published?
 
Question - The 12 V battery has been overcharged 10 times - what is overcharged. I wonder if there is a value published?
Yea, that struck me as odd. Not sure why the system would be overcharging the battery.

Swapped it out yesterday and all errors resolved. Couple oddities:

IMG_9732.jpeg


Old battery appeared to be swollen on the sides. This likely indicates overcharging.


IMG_9719.jpeg
IMG_9727.jpeg


The new battery came with marks on the posts and that odd green handwritten sticker. Any chance Tesla sold me a used battery? It works, so doesn't really matter either way I guess.

Btw, no core charge when buying from Tesla, so you can get $10 back from Autozone or the like which makes the Tesla branded battery an even better deal.
 
Yea, that struck me as odd. Not sure why the system would be overcharging the battery.

Swapped it out yesterday and all errors resolved. Couple oddities:

View attachment 769295

Old battery appeared to be swollen on the sides. This likely indicates overcharging.


View attachment 769296 View attachment 769298

The new battery came with marks on the posts and that odd green handwritten sticker. Any chance Tesla sold me a used battery? It works, so doesn't really matter either way I guess.

Btw, no core charge when buying from Tesla, so you can get $10 back from Autozone or the like which makes the Tesla branded battery an even better deal.
Good question for the service center but they may have tested it before sending it out. If the old battery case compared to the replacement was swollen, I would advise tesla so it can be put into a data base.
 
Good question for the service center but they may have tested it before sending it out. If the old battery case compared to the replacement was swollen, I would advise tesla so it can be put into a data base.

I suspect that's exactly it - they probably topped off the battery 12/31 and that's what the green sticker and witness marks on the posts are all about.
 
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Yea, that struck me as odd. Not sure why the system would be overcharging the battery.

Swapped it out yesterday and all errors resolved. Couple oddities:

View attachment 769295

Old battery appeared to be swollen on the sides. This likely indicates overcharging.


View attachment 769296 View attachment 769298

The new battery came with marks on the posts and that odd green handwritten sticker. Any chance Tesla sold me a used battery? It works, so doesn't really matter either way I guess.

Btw, no core charge when buying from Tesla, so you can get $10 back from Autozone or the like which makes the Tesla branded battery an even better deal.
The manufacture date is there on the sticker, July 19, 2021, so it's 7 months old, but the scratch marks on the posts seem to be more than I would expect from applying a top-off charge. Fresh batteries come with the red plastic covers.
 
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Yea, that struck me as odd. Not sure why the system would be overcharging the battery.

Swapped it out yesterday and all errors resolved. Couple oddities:

View attachment 769295

Old battery appeared to be swollen on the sides. This likely indicates overcharging.


View attachment 769296 View attachment 769298

The new battery came with marks on the posts and that odd green handwritten sticker. Any chance Tesla sold me a used battery? It works, so doesn't really matter either way I guess.

Btw, no core charge when buying from Tesla, so you can get $10 back from Autozone or the like which makes the Tesla branded battery an even better deal.
I'm wondering if the overcharge testing that was added to some of the more recent Tesla updates may have caused the bulging?
 
overkill. replace once out of warranty and otherwise have Tesla fix this issue on their own dime. OEM 12V battery should last at least 4yrs / 50k miles...
Maybe excessive towing costs/ mobile service dispatching will drive some "priority" at Tesla on ensuring something as mundane as a 12V battery doesn't crap out after 2yrs.
 
The manufacture date is there on the sticker, July 19, 2021, so it's 7 months old, but the scratch marks on the posts seem to be more than I would expect from applying a top-off charge. Fresh batteries come with the red plastic covers.
Yea, the scratch marks seemed to look more than what would have been done just by some alligator clips. And the missing red cover was suspect as well. Weird. I should have asked when I picked the battery up in retrospect.
 
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I proactively upgraded to the Ohmuu battery in my 2018 M3P at the end of last year, and glad that I did because the stock battery was starting to showing inconsistent readings when I tested it after replacement. Important to remember how winter weather strains batteries too depending on where you live, so I always test and replace as necessary before the winter gets too bad.

Problem is that I got the V11 update the very next day, and it tests the battery differently and brought back the battery fail error with Ohmuu batteries. Ohmuu is now developing a module that can update the battery to match what Tesla’s software is looking for. So I also have a cheap $80 BJ’s 51R in there now until they figure everything out. I’m all for the longevity of the lithium ion battery in the long run, so I’ll stick around and see what they come up with. Plus I swear that battery feels like a lunch box compared to the weight of the stock and cheap BJ battery. Don’t really care about the “weight savings” but it’s just funny how tossable the Ohmuu is if you’re not paying attention lol.

All my last cars before the M3P were tuners, so I always carry a full toolkit in the trunk and proactivity was burned into my head lol. My cars are my hobby, so I don’t mind the cost and extra work of proactivity so much.
 
I proactively upgraded to the Ohmuu battery in my 2018 M3P at the end of last year, and glad that I did because the stock battery was starting to showing inconsistent readings when I tested it after replacement. Important to remember how winter weather strains batteries too depending on where you live, so I always test and replace as necessary before the winter gets too bad.

Problem is that I got the V11 update the very next day, and it tests the battery differently and brought back the battery fail error with Ohmuu batteries. Ohmuu is now developing a module that can update the battery to match what Tesla’s software is looking for. So I also have a cheap $80 BJ’s 51R in there now until they figure everything out. I’m all for the longevity of the lithium ion battery in the long run, so I’ll stick around and see what they come up with. Plus I swear that battery feels like a lunch box compared to the weight of the stock and cheap BJ battery. Don’t really care about the “weight savings” but it’s just funny how tossable the Ohmuu is if you’re not paying attention lol.

All my last cars before the M3P were tuners, so I always carry a full toolkit in the trunk and proactivity was burned into my head lol. My cars are my hobby, so I don’t mind the cost and extra work of proactivity so much.
Waiting patiently as well…..running stock OEM in the interim. 2018 P3D+ been running the Ohmmu for 8 months. By the way (no biggie) but it’s 2 mm’s and 1 u.😁

Ski
 
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My car is at the 2 year mark, and since I am planning a trip to AZ next month, I decided to go ahead and schedule a mobile service appointment for a proactive battery replacement. Got a call from the service advisor confirming that I wanted the replacement, since they didn’t see any errors. I confirmed, and the appointment is set for next week. Cost before tax will be about $117.

He also mentioned that they would be updating the battery to the Lithium ion battery (he sad LED battery, but I think he meant Li-on, or maybe I misheard him). Will update back next week when I have it installed, but I didn’t realize that they were installing lithium batteries now.