replacement 12V batteries for 2018 M3: OEM or 3rd party "group 51r" ok?

[marcmerlin]

I already saw this thread which tells me not to buy the Ohmu lithium battery

Update on replacing OEM 12v lead-acid battery with lithium?

Tesla (unlike every other ICE car I've ever heard of) actually has a system to monitor voltage and detect when the battery is on it's way out long before it actually fails, in most cases. Every Honda made in the last several years with auto idle stop, for example, measures the internal...

teslamotorsclub.com

and

Q1: My battery is almost 5 years old, so I understand it went past its expected life. Not sure if it's best to get the exact same, or if 5 years later there is something a bit better? Can I find a better GLA 12V battery from a 3rd battery, maybe even cheaper, or am I better off going with the Tesla defaut OEM replacement?

Q2: right now I have a mobile service appt for a new battery this sunday. Is the price of service+battery reasonable (didn't get a quote due to thanksgiving), or am I better off going to some auto parts store and getting a group 51r battery, and swapping it myself?

I'm just a bit worried because I need my car to work for a few days and can't afford to be stranded if the current 12V battery really dies after I drive somewhere and park the car.

In the meantime, I got around the 12V low battery warnings by disconnecting the 12V battery, disconnecting the 200A DC-DC converter to reset the car and the 12V low message, and using a separate 6A 12V charger to boost the battery a bit back up. I know it's a temporary fix, but the good news is that it brought back the battery to 14V for now, so the car is happy and the "car may shut off while you're driving" message went away, and hopefully it will last long enough until I get the replacement battery.
On that topic, do you know why on earth the car would shut off when it's already started and the DC-DC converter is active and the car driving? Is that even a thing, or is that a fake warning that really means that if you park your car and the DC-DC shuts off, the 12V standby may be too low to allow reconnecting the DC-DC contactor, leaving you stranded, but not on the side of some freeway?

 

[3sr+buyer]

The summary from various threads is that any 51R battery will fit, but most are significantly more expensive than buying the Hankook Atlas BX from Tesla (even if you pay for installation), and most do not have the connection for the vent hose.

 

[dhrivnak]

Any group 51 should work and while I went to a local auto store I found out Tesla is about 1/2 the price I paid. Strange but true.

 

[RayK]

I initially thought that I'd install the Ohmmu Li-ion battery once the factory 12V battery died but I changed my mind after reading about some of the difficulties involved. So, just short of 4 years old and around 24K miles, I had it proactively replaced by mobile service (~$120 parts and labor in June 2022). The factory 12V battery appears to have the lowest cost of any 51R battery (~$75).

 

[miimura]

On that topic, do you know why on earth the car would shut off when it's already started and the DC-DC converter is active and the car driving? Is that even a thing, or is that a fake warning that really means that if you park your car and the DC-DC shuts off, the 12V standby may be too low to allow reconnecting the DC-DC contactor, leaving you stranded, but not on the side of some freeway?

If the DC-DC converter in the PCS is healthy, the car should not shut off when driving because the energy is all coming from the PCS anyway. The most common failure mode is the car failing to start up or charge the 12V battery when parked. When the car detects that the 12V battery is failing, it will usually increase the frequency of recharging the 12V and may, in some cases, never go to sleep and keep the car powered from the traction battery and PCS. However, you should not count on this and get the 12V replaced as soon as there is any indication that it's failing. The price from Tesla is very reasonable for what you're getting and I see no reason to deviate from that with a lithium battery or even an AGM from different supplier.

Our April 2018 Model 3 is still on the factory original 12V battery with no indication of impending failure. However, I am prepared to rescue the car on short notice.

 

[nicksp]

Tesla charged me $120 out the door. Installed in my own home. Can't get any more reasonable than that.

 

[JDubs]

Tesla charged me $120 out the door. Installed in my own home. Can't get any more reasonable than that.

Was it an in or out of warranty replacement?

 

[RayK]

Was it an in or out of warranty replacement?

If Tesla charged $$$ for the 12V battery, it was not under warranty. Either the 4yr/50K mile warranty expired or the battery was requested to be replaced (i.e., it did not fail or was flagged by the software as being bad).

 

[nicksp]

Was it an in or out of warranty replacement?

Out of warranty on my 18 M3LR

 

[marcmerlin]

If the DC-DC converter in the PCS is healthy, the car should not shut off when driving because the energy is all coming from the PCS anyway. The most common failure mode is the car failing to start up or charge the 12V battery when parked. When the car detects that the 12V battery is failing, it will usually increase the frequency of recharging the 12V and may, in some cases, never go to sleep and keep the car powered from the traction battery and PCS. However, you should not count on this and get the 12V replaced as soon as there is any indication that it's failing. The price from Tesla is very reasonable for what you're getting and I see no reason to deviate from that with a lithium battery or even an AGM from different supplier.

Our April 2018 Model 3 is still on the factory original 12V battery with no indication of impending failure. However, I am prepared to rescue the car on short notice.

thanks for confirming my understanding. Yes, I was definitely going to change the battery, but since it happened on thanksgiving, I had to limp along for a few days. Tesla replaced it for $125 onsite, which probably is barely break even for them.

 

[Rocky_H]

right now I have a mobile service appt for a new battery this sunday. Is the price of service+battery reasonable

Very reasonable. It's interesting people spend so much time and effort trying to go other places to try to find batteries that kinda may possibly work because they assume it's a better deal than the manufacturer, but in this particular instance, it's fine just to have Tesla do it for cheaper with one that is known to work. I priced a windshield replacement earlier this year, and it was half as much from Tesla as from Safelite, which surprised me. Their rates aren't bad on a lot of stuff.

And a 12V battery technically should be considered a wear item, like wiper blades or brake pads that should be on your own dime anyway, but Tesla has for a very long time basically done this as goodwill during the warranty period.

 

[3sr+buyer]

In general, it looks like buying a replacement 12V battery from Tesla is the safest and cheapest option.

Awareness of other options may only be for the case where Tesla is not accessible in the needed time frame (e.g. out of stock). The vent hose fitting would be the main concern other than the price if it came to that.