12 volt battery "back-up?"

[longshadows]

I've read a few times about problems some owners have had with the 12 volt batteries (near the frunk) and some have had to replace them, some even carry a replacement... "just in case." What's the deal? Is this a serious issue and how should a concerned owner deal with this possibility? I'm especially concerned, as I don't live near a Tesla Service Center and who knows how long it might take a Mobile SC to get to coastal Maine. Thanks.

 

[jjrandorin]

I asked a similar question (how to maintain the 12 volt battery) to a poster who is a tesla mobile ranger. Basically, he said that the 12 volt does not take trickle charging, but gets plenty of charging from the high voltage battery when plugged in nightly as recommended.

I havent seen anyone say they are carrying replacement 12 volt batteries "just in case". Where are you seeing that?

 

[longshadows]

I havent seen anyone say they are carrying replacement 12 volt batteries "just in case". Where are you seeing that?

Actually, I misspoke. I can't say that I've seen owner say they carry a backup, but one of the popular Tesla "third-party" EVTuning Solutions sells them, with the following "just in case" statement, implying that it's something we should consider:

Are you tired of seeing the dreaded "12v Battery Needs Replacement"?
Has your car left you stranded during the cold winter months?
Do you want to skip adding an auxiliary battery to install your dashcam?
These Lithium Replacement 12v Batteries for Model S/X/3 are a great upgrade!
Integrated Battery Management System and 48 Month Full Replacement Warranty!
Also includes FREE SHIPPING!!

​

Thank you.

 

[jjrandorin]

Ok, a vendor who sells the battery having that in the description makes more sense. They are trying to sell products. Not saying it cant happen, I have read a few things about various things that happen when the 12 volt battery is low.

The mobile ranger said that we cant trickle charge it and I have no reason to doubt him. He said it CAN be jump started, but not trickle charged. If you plug in as recommended in the manual when the car is at home, you will likely be ok.

All batteries eventually wear out, and ICE cars have issues when the battery goes dead too. If it really bothers you, I suppose you could buy a backup 12v to keep in your garage or something... but by the time you use it, it could also go bad from just sitting.

 

[longshadows]

Ok, a vendor who sells the battery having that in the description makes more sense. They are trying to sell products. Not saying it cant happen, I have read a few things about various things that happen when the 12 volt battery is low.

The mobile ranger said that we cant trickle charge it and I have no reason to doubt him. He said it CAN be jump started, but not trickle charged. If you plug in as recommended in the manual when the car is at home, you will likely be ok.

All batteries eventually wear out, and ICE cars have issues when the battery goes dead too. If it really bothers you, I suppose you could buy a backup 12v to keep in your garage or something... but by the time you use it, it could also go bad from just sitting.

Yes, my thoughts exactly. Thanks for the feed back.

 

[ohmman]

The problem with Tesla and 12V batteries is pretty well documented. I don't know if they've changed anything for the Model 3, but in the S and X it's all about deep cycling. Tesla has excellent BMS for the high voltage battery but they abuse the 12V quite a bit. Many people have reported near-annual replacement. My personal experience has been that my S battery has lasted almost 5 years (I just got the alert this week for the first time and the car will be 5 in March). My X battery needed replacing after 2 years.

 

[brkaus]

You can put a trickle charger on it if you want to reduce the cycling. Of course, then you have another plug to connect/disconnect.

My previous ICE cars have left me stranded with dead batteries. It happens.

 

[ewoodrick]

The only thing that you should really know is where the battery is and how to get to it if it is dead. Carrying an extra battery is overkill and paranoia.

 

[scottm]

The problem with Tesla and 12V batteries is pretty well documented. I don't know if they've changed anything for the Model 3, but in the S and X it's all about deep cycling. Tesla has excellent BMS for the high voltage battery but they abuse the 12V quite a bit. Many people have reported near-annual replacement. My personal experience has been that my S battery has lasted almost 5 years (I just got the alert this week for the first time and the car will be 5 in March). My X battery needed replacing after 2 years.

From facelift model S forward, Tesla has added an "always on" trickle charger from the big battery to float the little battery. This is happening while parked and not plugged in. This means, while parked there's no need for the car to trigger a contactor closure and deep cycle 12v recharge from discharged state.

The Tesla trickle charge is still a vampire drain, keeping the resting 12v electronics alive, but is feeding off the main pack .. reducing range.

With my older S, while parked at home I plug in an external 12v trickle charger (always connected to battery boost posts) all the time. This keeps away about 4 to 6 deep cycles per day. I'm on my original 12v battery. I devised this to keep down contactor wear, and to avoid deep cycling and 12v replacements, and to keep range of the car exactly where I left it when I parked. My added trickle charger prevents vampire drain of the main pack, keeping 12v electronics alive from the wall. Taking about 21 watts from the wall 120V outlet. FYI my car settings are "always awake" and "always connected". I seldom charge the S at home anymore... charge all day at work on just 120V - which keeps contactors closed all day and Tesla's electronics trickling the 12v at the same time the main pack is charging. This is about as much as you can possibly do babying the 12v battery and contactors in older S... I'm into this car for the long haul and want to keep my off-warranty expenses down.

The model 3 we just plug in at main charger port when it's home. Or not. I guess we could figure a way to add an external trickle charger to the 3 to prevent vampire drain of main pack.. but meh. The 12V is taken care of by Tesla's trickle and if the car is plugged in, it gets juice via the route of the main pack and that power cord... same juice either way. I don't hear a lot of clacking of contactors on the 3 while parked.. it's an aggressive sleeper and also allows a few % run down of the main pack before topping up to charge set point. So I'm not worried about contactor wear. And I expect the 12v in the 3 to last as well as my babied model S 12v.

tl;dr version:

Tesla definitely addressed the main problems with the 12v chassis power architecture in the model 3. Plug the car in and rest easy.

They have a ways to go yet with reducing the idle power consumption of devices in the car. I fear the engineers feel that sitting on top of a big fat tractor pack has taken their eye off the ball of power conservation and good low power designs, using extensive sleeps and low power modes of devices. Their brains must be in the "power is cheap" space.

 

[NeverFollow]

I've read a few times about problems some owners have had with the 12 volt batteries (near the frunk)
and some have had to replace them, some even carry a replacement... "just in case."

What's the deal? Is this a serious issue and how should a concerned owner deal with this possibility?
I'm especially concerned, as I don't live near a Tesla Service Center
and who knows how long it might take a Mobile SC to get to coastal Maine. Thanks.

I wish there was an easy way to control the 12 V battery status.

I put a small and very convenient 12 V Outlet to get USB fast charge and also to display the 12 V voltage

I also carry a small 12 V Car Jump Starter "Just in Case" but I mostly used to help ICE with dead 12 V battery
and used it also for my Laptop with a 120 V 2000W Sine Inverter.

 

[scottm]

Hey @NeverFollow What voltage do you normally see at the lighter outlet? I suspect something in 14v range..

When you turn the car off, it drops to zero, right?

 

[jjrandorin]

On trickle charging the model 3, please see the following thread, starting at post #61 where I asked poster "mobile ranger" who identified himself as a tesla mobile ranger doing an AMA style Q&A session a question about trickle charging the battery:

Mobile Ranger here, ask me (almost) anything!


TL ; DR his answer was: "you can not trickle charge the model 3 12v battery but you can jump it..".

Just passing on what his response was.

 

[NeverFollow]

Hey @NeverFollow
What voltage do you normally see at the lighter outlet? I suspect something in 14v range..

When you turn the car off, it drops to zero, right?

That's right, I was going to mention it. Thank you for asking.

Yes, I can see 14 V and it turned off when the car is locked.

I connect my Blackvue DR900 dash cam to it.

Note: I would recommend another model: 12 V Outlet to get USB fast charge because the reading was a little bit difficult.

 

[BerTX]

On trickle charging the model 3, please see the following thread, starting at post #61 where I asked poster "mobile ranger" who identified himself as a tesla mobile ranger doing an AMA style Q&A session a question about trickle charging the battery:

Mobile Ranger here, ask me (almost) anything!


TL ; DR his answer was: "you can not trickle charge the model 3 12v battery but you can jump it..".

Just passing on what his response was.

It is a lead-acid battery. It can be trickle charged. I think maybe the Ranger meant it wouldn't do any good. Perhaps it would harm some system in place on newer cars, I don't know. But the battery CAN be charged.

 

[BerTX]

From facelift model S forward, Tesla has added an "always on" trickle charger from the big battery to float the little battery. This is happening while parked and not plugged in. This means, while parked there's no need for the car to trigger a contactor closure and deep cycle 12v recharge from discharged state.

The Tesla trickle charge is still a vampire drain, keeping the resting 12v electronics alive, but is feeding off the main pack .. reducing range.
...

This is the first I have heard of this change. Do you have a source where I can read more about it? I wonder how much difference it is making in 12V longevity. I have a 2 year old facelift MS and have been studying the options to replace the battery soon, but maybe I don't need to worry.

 

[jjrandorin]

It is a lead-acid battery. It can be trickle charged. I think maybe the Ranger meant it wouldn't do any good. Perhaps it would harm some system in place on newer cars, I don't know. But the battery CAN be charged.

I can only go by what mobile ranger said, which I will copy and paste the relevant discussion so people wont have to read another link

@Mobile Ranger

I know a day has passed, but if you are still open for questions I have another one. I have a cTek branded trickle charger (battery charger) that I had for my BMWs. The charger specifically supports AGM style batteries as thats what modern BMWs use.

Do you recommend that consumer / end users put the 12v on a trickle charger or does it receive "enough" charging from being plugged into a home charger (I have the Tesla HPWC on a 60 amp circuit). In BMWs, monthly or so trickle charging of the AGM battery extended the life of said battery.

Since it appears that low 12v in teslas can cause all sort of issues, I am looking to avoid that as much as possible.

If this is proprietary info, feel free to ignore.

The 12v can be jump stated, but not trickle charged. Your larger battery helps maintain your 12v, so keeping it plugged in for charging overnight should be good!

 

[BerTX]

I can only go by what mobile ranger said, which I will copy and paste the relevant discussion so people wont have to read another link

Thinking is hard.

 

[Olds442]

when my 12v battery required "service" on the '13 P85 tesla service sent a ranger (don't think they call them that any longer) and he swapped out the battery in my driveway. that's not easy on an early 2013 as the 12v is way down in the frunk, he commented how it's a lot easier on the newer cars.

being curious i asked what this would have cost me if i wasn't still under warranty. he said "about $220".

i laughed, seriously? $220? a decent 12v battery costs $140-150 so add another $70 for labor and I get to watch from the living room. i'll take that deal every time, i hate working on cars in the winter.

also of note, the car was operable the entire time so there was no loss of use while waiting for them to get the battery and schedule an install time/date. i can't see why you'd ever have to carry a back up but others may have experienced complete failures. i didn't.

 

[TexasEV]

To the OP, if you want to come up with a reason to not buy a Model 3, I suppose this is as good as any. But know that something can go wrong in any car, and probably >99.9% of Model 3 owners have never had an issue with the 12V battery. It’s just not something anyone thinks about except a handful of owners who post here, out of tens of thousands, and even most of them never had the problem rather they’re just theorizing.

 

[ChrisH]

The problem with Tesla and 12V batteries is pretty well documented. I don't know if they've changed anything for the Model 3, but in the S and X it's all about deep cycling. Tesla has excellent BMS for the high voltage battery but they abuse the 12V quite a bit. Many people have reported near-annual replacement. My personal experience has been that my S battery has lasted almost 5 years (I just got the alert this week for the first time and the car will be 5 in March). My X battery needed replacing after 2 years.

The car alerted you that the 12V needed replacement?