How urgent is "12V battery degraded" warning?

[EVRider-FL]

Today my wife's Model 3 displayed a dialog saying the 12V battery has degraded and should be serviced. The car is 3 years old, so I know it's not unusual to have to replace the battery at this point, but I was wondering how urgent the replacement is. There have been no symptoms of 12V battery issues, and this is the first time that message appeared.

I scheduled a service appointment, but the only available dates (for mobile service) were while we're out of town. Any reason this couldn't wait until January if we don't drive much before then? I'll keep the car plugged in while we're out of town.

 

[OUengineer]

Have the same issue right now. Was about to buy the battery and install it myself (out of warranty car) but Tesla SC told me that the new battery needs to be calibrated by them or it may fall again in around 6 months! I'm a little sceptical about that.

Any new car needs the computer to be aware of the battery specs and the age of the battery. It will charge differently as the battery ages. If it still thinks an old battery is installed, it may give too much juice to the new battery on a regular basis or something to that effect.

I don't know if Tesla does any actual battery specific calibration tho. On other cars, you have to have a dealer reset the computer for a new battery (unless you have an OBD connection port and software to change the ECU coding)

 

[iwannam3]

Don't believe the "warning will let you know" Most failures are sudden and no warning.

 

[iwannam3]

Any new car needs the computer to be aware of the battery specs and the age of the battery. It will charge differently as the battery ages. If it still thinks an old battery is installed, it may give too much juice to the new battery on a regular basis or something to that effect.

I don't know if Tesla does any actual battery specific calibration tho. On other cars, you have to have a dealer reset the computer for a new battery (unless you have an OBD connection port and software to change the ECU coding)

Battery charging voltage is based on temperature, if they are so clever to do something different based on the age, why do the batteries fail so quick? If I disconnect and reconnect the same battery does it think it is a new battery? Has anyone see a ranger "calibrate" something to the new battery?

 

[dmurphy]

Any new car needs the computer to be aware of the battery specs and the age of the battery. It will charge differently as the battery ages. If it still thinks an old battery is installed, it may give too much juice to the new battery on a regular basis or something to that effect.

I’m very sorry to see what BMW must have put you through in a past life. Glad you’re no longer in that abusive relationship. What they do with “registering” a battery to a car is just plain odd, and has always smacked of a dealer-profiting system rather than anything technical to me.

I’ve never owned any car that needs a “calibration” to its 12V battery. Install, drive. That’s, uh, it.

Same on Model 3 as every other vehicle I’ve ever owned. Install and go.

 

[iwannam3]

I’m very sorry to see what BMW must have put you through in a past life. Glad you’re no longer in that abusive relationship. What they do with “registering” a battery to a car is just plain odd, and has always smacked of a dealer-profiting system rather than anything technical to me.

I’ve never owned any car that needs a “calibration” to its 12V battery. Install, drive. That’s, uh, it.

Same on Model 3 as every other vehicle I’ve ever owned. Install and go.

OMG! It is true! Here is a vendor selling a cable to hook to your BMW to your laptop with their purchased software and schedule an appointment for their tech to access your car when you have install your new battery! Says it saves a lot of money compared to having the dealer do it. I believe it! And if you don't all sorts of gremlins will haunt your BMW. At this point I am surprised putting in a non BMW branded battery doesn't void the warranty.
From another website selling the "service": If the car’s alternator is constantly running, driven by the engine via a drive belt to keep the battery charged up, that would mean a continuous load is being placed on the engine. The load on the engine, albeit relatively small, does add up over the many hours you operate the car, day in and day out. To boost fuel economy, the BMW ECU is programmed to drive the alternator intermittently, only when electrical consumption truly necessitates it.

Keep in mind the dealer typically charges about $215 in labor alone for replacement and registration (1.5HR at $143.5/HR), BATTERY EXTRA $$

The best way to keep a battery alive is a continuous trickle charge. Tesla seems to do it like BMW, letting it discharge and then hitting it with a high charge rather than a continuous maintenance charge. that's why our batteries die early. I would expect that BMW would require you to stop by their service center to have every tank of gas tested for octane and get the BMW optimizer additive to maximize engine power.

 

[android04]

OMG! It is true! Here is a vendor selling a cable to hook to your BMW to your laptop with their purchased software and schedule an appointment for their tech to access your car when you have install your new battery! Says it saves a lot of money compared to having the dealer do it. I believe it! And if you don't all sorts of gremlins will haunt your BMW. At this point I am surprised putting in a non BMW branded battery doesn't void the warranty.
From another website selling the "service": If the car’s alternator is constantly running, driven by the engine via a drive belt to keep the battery charged up, that would mean a continuous load is being placed on the engine. The load on the engine, albeit relatively small, does add up over the many hours you operate the car, day in and day out. To boost fuel economy, the BMW ECU is programmed to drive the alternator intermittently, only when electrical consumption truly necessitates it.

Keep in mind the dealer typically charges about $215 in labor alone for replacement and registration (1.5HR at $143.5/HR), BATTERY EXTRA $$

The best way to keep a battery alive is a continuous trickle charge. Tesla seems to do it like BMW, letting it discharge and then hitting it with a high charge rather than a continuous maintenance charge. that's why our batteries die early. I would expect that BMW would require you to stop by their service center to have every tank of gas tested for octane and get the BMW optimizer additive to maximize engine power.

Just want to point out that Tesla does not (currently) allow the 12v battery to drain ever if the car is awake. It's always being charged or maintained at float voltage. The only time the Tesla 12v battery is being allowed to drain is when the car is asleep. I've been measuring my 12v system since around August 2021 on my Model 3 and it never gets below 97-98% of the stated Ah capacity on it.

 

[iwannam3]

Just want to point out that Tesla does not (currently) allow the 12v battery to drain ever if the car is awake. It's always being charged or maintained at float voltage. The only time the Tesla 12v battery is being allowed to drain is when the car is asleep. I've been measuring my 12v system since around August 2021 on my Model 3 and it never gets below 97-98% of the stated Ah capacity on it.

There was supposed to be at some point new BMS for the lead acid battery. Time will tell if batteries stop failing at 2 to 3 years.

 

[Watts_Up]

Just want to point out that Tesla does not (currently) allow the 12v battery to drain ever if the car is awake. It's always being charged or maintained at float voltage. The only time the Tesla 12v battery is being allowed to drain is when the car is asleep. I've been measuring my 12v system since around August 2021 on my Model 3 and it never gets below 97-98% of the stated Ah capacity on it.

@android04 I would be interested to know how your detrmine the Ah capacity?

I wonder if you are measuring the voltage of the battery or if you realy have a device
measuring the current going to the battery and also the current going out of the battery,
using an Amp Meter with a Shunt or an Hall effect sensors?

 

[android04]

@android04 I would be interested to know how your detrmine the Ah capacity?

I wonder if you are measuring the voltage of the battery or if you realy have a device
measuring the current going to the battery and also the current going out of the battery,
using an Amp Meter with a Shunt or an Hall effect sensors?

I fully charged the lead acid battery while disconnected from the Tesla with a smart battery charger/maintainer. I did that before connecting the 12v battery monitor that I'm using, and calibrated it to show that the battery was at 100% charge at the time. Then I set the battery capacity of 45Ah because that is what the OEM battery shows on its label (and also what the manufacturer's spec sheet shows).

So when I look at my battery monitor, it will show me the voltage of the battery, the current going into or out of it, the charge level in %, and the remaining capacity in Ah.



Edit to add that I've had this installed since August of 2021 and I've definitely noticed changes in charging voltages based either on outside temperature (lead acid charging voltage should change based on temperature), and based on software updates.

 

[walnotr]

My car may be the outlier, but I am still on the original battery after almost four years. I’ve been waiting for the alert but have yet to see it.

 

[android04]

My car may be the outlier, but I am still on the original battery after almost four years. I’ve been waiting for the alert but have yet to see it.

My car is on the original too, since 03/2018 and 78,500 miles. I think the ones that suffer failure tend to be more vocal about it. Although my battery is also a different part number and it's unknown what changed between mine (revision -A) and all the batteries from about 04/2018 that have all been revision -B.

 

[KuramaKitsune]

I checked on the car again and this time it turned on, but with a warning about the low battery and limited functionality. I was able to move the car out of the garage so it will be easier to service (or tow) tomorrow. Contacted Roadside Assistance earlier today and they'll try to get mobile service here tomorrow.

so we are talking about a 24 hour warning ?

 

[EVRider-FL]

so we are talking about a 24 hour warning ?

In my case, yes.

 

[gearchruncher]

I’m very sorry to see what BMW must have put you through in a past life. Glad you’re no longer in that abusive relationship. What they do with “registering” a battery to a car is just plain odd, and has always smacked of a dealer-profiting system rather than anything technical to me.

BMW uses AGM batteries, and these have a well known and proven voltage vs state of health curve. The battery will absolutely last longer if treated the way BMW treats it. The trick is that there's no way for the car to know you replaced a battery, so you need a tool to tell the computer (and also tell if if you changed battery size). If you don't do this, the car will apply too much voltage to the new battery and shorten it's lifespan.

Yes it's unique, and maybe not worth it, but this is a case of Germans over-engineering a system, not adding something just for profit.

Anecdote: I had a BMW with a 13 year old OEM battery in it when I sold the car, was still working fine.

 

[gearchruncher]

On a completely different note, Tesla changed their 12V battery management pretty drastically at the end of 2021 with a software update. Behaviors and ability to detect a bad battery from before then may not be the same as now.

 

[jsmay311]

Just want to point out that Tesla does not (currently) allow the 12v battery to drain ever if the car is awake. It's always being charged or maintained at float voltage. The only time the Tesla 12v battery is being allowed to drain is when the car is asleep.

On a completely different note, Tesla changed their 12V battery management pretty drastically at the end of 2021 with a software update. Behaviors and ability to detect a bad battery from before then may not be the same as now.

I just got a 12V battery warning on my 5-year-old Model 3 yesterday.

There were 3 warning/error messages that it cycled through and one of them said “Vehicle will consume more energy while idle”. And now it appears that the car will not go to sleep. (I have TeslaFi and can see that it’s been awake for the past 12 hours.)

Is this message and behavior new vs 2021? Or was it always this way?

If it’s new, is keeping the car awake 24/7 and therefore keeping the HV-to-12V DC-DC converter active continuously the aforementioned “fix” that Tesla implemented to keep the car drivable for longer periods after the 12V battery starts to die?

(This is relevant to me because the earliest service appointment I can get to have Tesla replace the 12V battery is 4 days away with a mobile tech. (For $113.20 total, btw.) But if waiting that long would be risky, I could try to pick up a battery from the service center sooner and try the DIY route.)

 

[gearchruncher]

Is this message and behavior new vs 2021? Or was it always this way?

If it’s new, is keeping the car awake 24/7 and therefore keeping the HV-to-12V DC-DC converter active continuously the aforementioned “fix” that Tesla implemented to keep the car drivable for longer periods after the 12V battery starts to die?

(This is relevant to me because the earliest service appointment I can get to have Tesla replace the 12V battery is 4 days away with a mobile tech. (For $113.20 total, btw.) But if waiting that long would be risky, I could try to pick up a battery from the service center sooner and try the DIY route.)

Yes, this is a fairly new behavior, since mid or late 2022.

You will get tons of opinions on how urgent this is. There's a 29 page thread here:

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

The only "major" service issue I have ever had with my 2018 P3D is that I had to have the 12v battery replaced after about 2 1/2 years. Even though it was covered under warranty, I consider it a major issue because it rendered the car undriveable and it had to be towed. At that time, there was...

teslamotorsclub.com

In my opinion, you are fine. The car flat out can't die unless it goes to sleep, and as you saw it won't do that anymore. Your battery is not dead, just wearing out. A few more days is irrelevant.

 

[brkaus]

Yes it's unique, and maybe not worth it, but this is a case of Germans over-engineering a system, not adding something just for profit.

They could have easily put it on a menu within the car.

 

[gearchruncher]

They could have easily put it on a menu within the car.

Like every car manufacturer could do for every service function they have?
I assume you are equally annoyed Tesla doesn't give you access to the brake bleeding functions or gateway configs?

 

[brkaus]

Like every car manufacturer could do for every service function they have?
I assume you are equally annoyed Tesla doesn't give you access to the brake bleeding functions or gateway configs?

Yes, of course. I am happy they added a few to the service menu - coolant purge for example.