12V battery hocus pocus?

[postman]

I’m wondering how Tesla decides to give you the “low voltage battery needs to be replaced” message.

I have a 2018 M3 LR RWD, and I got the warning last night. The battery is the factory one, so about 60-63 months old. Seemed reasonable.

I have a trip planned this week before I could get the Ranger out to do a replacement (FWIW, it was quoted at only about $115 installed), so I hustled down to the SC a hundred miles away, picked one up, and popped it in this afternoon.

I took the old one down to the local NAPA store to put in in their core pile. The salesperson said it looked like a new battery (it was pretty clean), and ran a battery test on it.

It came back just fine (see tester screen below). 12.6V, 303 CCA, good shape.

As noted earlier, 5 years on a lead-acid battery is pretty good, even with the lack of hard cranking to drain the battery.

So…any ideas what the criteria for Tesla generating the message is?

 

[dafish]

Given the heartburn that folks report when they totally fail unexpectedly I would shrug my shoulders and replace

 

[RayK]

Not sure but I think it has to do with the charging profile (i.e., how often and long a charge is needed to "top off" the battery).

Q: If you're in Livermore, then there should be a Tesla Service center in Dublin. Only about 15-20 miles, not 100. Why not go there?

 

[E90alex]

Determining lead acid battery health is not very accurate. Hence why they often fail with no warning.

 

[gearchruncher]

There's a 30 page thread on this:

"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

A test at an auto store is checking that it can crank an engine for 5 seconds. That has nothing to do with how a Tesla uses a battery. Tesla drains it and charges it slowly.

Trust the highly engineered Tesla test. Oh, and you removing it from the car? That reset the test, and now you have a much higher chance of it failing, because once the car detects the failure, it protects against it by using the HV battery to back it up. But now when you put it back in, it will think it's new and healthy and if it fails it won't be in protection mode.

 

[postman]

There's a 30 page thread on this:

"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

A test at an auto store is checking that it can crank an engine for 5 seconds. That has nothing to do with how a Tesla uses a battery. Tesla drains it and charges it slowly.

Trust the highly engineered Tesla test. Oh, and you removing it from the car? That reset the test, and now you have a much higher chance of it failing, because once the car detects the failure, it protects against it by using the HV battery to back it up. But now when you put it back in, it will think it's new and healthy and if it fails it won't be in protection mode

I did replace it with the new one; was just curious about how the determination was made (Did you read the originals post, or just load up the flamethrower with the above?).

 

[postman]

Not sure but I think it has to do with the charging profile (i.e., how often and long a charge is needed to "top off" the battery).

Q: If you're in Livermore, then there should be a Tesla Service center in Dublin. Only about 15-20 miles, not 100. Why not go there?

Need to update my profile; in San Luis Obispo now. We’re getting a SC, but it’s still under construction. The ride to Santa Barbara is pretty nice….

 

[postman]

Given the heartburn that folks report when they totally fail unexpectedly I would shrug my shoulders and replace

Yup. That’s what I did.

 

[ucmndd]

Cold cranking amps is not a particularly useful or relevant metric for testing a deep cycle battery used to power accessory systems in an EV.

ICE batteries need to provide high amperage for a very short amount of time to start an engine.

Low voltage EV batteries need to provide low amperage power for an extended period between charges by the HV system, so energy capacity is more important. I suspect Tesla throws the replacement alert message when the time needed between recharges consistently drops below a programmed threshold.

 

[3sr+buyer]

It came back just fine (see tester screen below). 12.6V, 303 CCA, good shape.

303 CCA seems to be a lot lower than what most new 51R batteries have (mostly 500 CCA, though there are some with 410 CCA). So the battery is significantly weaker than new, although it may not be weak enough to be completely failed.

 

[Cosmacelf]

I have had several batteries in my old ICE pass those tests, yet I knew were about to fail (and did, the one time I believed the test). Those store tests are worthless IMHO.