Near annual replacement of 12V battery is typical according to Tesla Service Tech

[AmpedRealtor]

I had my first 12v replaced within the first year, now am around 2 1/2 years and the replacement battery seems to be doing fine.

I should think that the 12v would be covered under warranty or annual service plan, I don't see the battery excluded from the annual service.

 

[miimura]

That doesn't sound right. The DC/DC should be active any time the DC load pulls the 12V battery down low enough, and there is more DC load when driving than when not.

I believe you are wrong. The DC/DC should be on and floating just over 14VDC whenever the car is driven or charging. That is NOT cycling the battery.

 

[Cottonwood]

That doesn't sound right. The DC/DC should be active any time the DC load pulls the 12V battery down low enough, and there is more DC load when driving than when not.

It is the discharge, charge cycling when the Tesla is off that wears out the 12V battery. If the Tesla is powered up to drive or charge the traction battery, the DC-DC converter is active and carries the full 12/14V load; the 12V battery is not discharged at those times and therefore has less wear.

If you spend more time driving and charging the traction battery, then the 12V battery is used less.

 

[dgpcolorado]

It is the discharge, charge cycling when the Tesla is off that wears out the 12V battery. If the Tesla is powered up to drive or charge the traction battery, the DC-DC converter is active and carries the full 12/14V load; the 12V battery is not discharged at those times and therefore has less wear.

If you spend more time driving and charging the traction battery, then the 12V battery is used less.

Does that suggest that charging more slowly (lower amperage) for longer on a routine basis would be better for the 12V battery? Something I hadn't thought about...

 

[Cottonwood]

Does that suggest that charging more slowly (lower amperage) for longer on a routine basis would be better for the 12V battery? Something I hadn't thought about...

I guess that is one of the few advantages of charging on 120 Volts. Because you are charging the traction battery a lot more, that reduces the number of discharge/charge cycles on the 12V battery. Pretty inefficient though...

The real solution is for Tesla to put a spike through the heart of the vampire and redesign the standby control circuits to use 1/10 or less of what they do now. Until then, they need to pony up and pay for 12V battery replacement for the life of the car.

It was Tesla's poor design in this area that created the problem. It's far cheaper for them to pay for replacement 12V batteries for the life of the cars than to replace the poorly designed hardware that is still shipping almost 4 years later. The 12V battery replacement for life is a cost that Tesla should just write off. Maybe that would motivate them to do the design correctly someday.

 

[dgpcolorado]

I guess that is one of the few advantages of charging on 120 Volts. Because you are charging the traction battery a lot more, that reduces the number of discharge/charge cycles on the 12V battery. Pretty inefficient though...

The real solution is for Tesla to put a spike through the heart of the vampire and redesign the standby control circuits to use 1/10 or less of what they do now. Until then, they need to pony up and pay for 12V battery replacement for the life of the car.

It was Tesla's poor design in this area that created the problem. It's far cheaper for them to pay for replacement 12V batteries for the life of the cars than to replace the poorly designed hardware that is still shipping almost 4 years later. The 12V battery replacement for life is a cost that Tesla should just write off. Maybe that would motivate them to do the design correctly someday.

I was thinking more about charging at 24 amps, as opposed to 40 or 80, not really slow charging at 120 V, 12 A. Increasing charge times several hours a day might help some.

Fixing the vampire drain aside, wouldn't a MUCH better solution be to use a Li-ion 12 V battery? Yes, much more expensive upfront, but Li-ion batteries like being in the middle range of charge state. No need to keep it fully charged all the time as with lead-acid.

 

[FlatSix911]

I was thinking more about charging at 24 amps, as opposed to 40 or 80, not really slow charging at 120 V, 12 A. Increasing charge times several hours a day might help some.

Fixing the vampire drain aside, wouldn't a MUCH better solution be to use a Li-ion 12 V battery? Yes, much more expensive upfront, but Li-ion batteries like being in the middle range of charge state. No need to keep it fully charged all the time as with lead-acid.

Agreed. A Li-ion 12V battery is the way to go ... see this thread: Lithium Ion 12v battery?

 

[chriSharek]

$53 is a cheap 12V. I just put one in the wife's Jeep and it was $150 (came with a 3 year warranty too though)

- - - Updated - - -

And I'll brag just a bit, my 2011 Volt's 12V battery is still functioning just fine - after almost 5 years and 88,000 miles . . .

I'm sure some folks aren't GM fans on the forum here, but their engineering of their products are absolutely stellar! Marketing, business tactics, and hands in deep oil pockets aside . . . .

 

[JRP3]

I believe you are wrong. The DC/DC should be on and floating just over 14VDC whenever the car is driven or charging. That is NOT cycling the battery.

It is the discharge, charge cycling when the Tesla is off that wears out the 12V battery. If the Tesla is powered up to drive or charge the traction battery, the DC-DC converter is active and carries the full 12/14V load; the 12V battery is not discharged at those times and therefore has less wear.

If you spend more time driving and charging the traction battery, then the 12V battery is used less.

Interesting. On my car I set the DC/DC to always run at the same voltage, unless I disconnect everything for longer term storage. Seems as if the easiest solution for Tesla is to have the DC/DC on more of the time when the car is turned off, so that voltage doesn't drop so low on the 12V battery. Maybe float it at 13V or so. Although it does sound as if the 12V battery is lasting much longer these days, so maybe they've increased the low voltage cut in point for the DC/DC, or maybe the reduced vampire has cut cycling enough so that it's acceptable with the better 12V battery.

 

[CSFTN]

data point to add to the others....
I have a 11.5 month old P85D. I have driven only about 7K miles in that time, I have a HPWC in the garage and I charge to 80-85% essentially every night. I have supercharged about 6 times, I have charged to 100% about 10 times, I have NEVER gone lower than 50% except on my 3 long distance trips, when I was driving. So, its never sat for a prolonged period of time, vamping the 12V away. I live in the South, and we have had a very warm winter. None of my previous cars had a battery die at <5 years. I have made no modifications, don't have a radar detector or a camera system; nothing is consuming the 12V battery except the normal car issues. I was in Florida for the past 5 days, I did neglect to plug in before I left, so over 4 days my car vamped down about 1% per day, down to about 55%. I plugged in last PM; I took it to pick up dinner tonight and was greeted by the "Your 12V battery needs servicing soon" warning.

So, it would appear even the Q1 2015 P85Ds still have not resolved the 12V battery issue.

 

[Steve S]

I'm glad it happened today instead of next week when I have a cross country trip planned. Calling Tesla tomorrow but my nearest SC is 3 hours away.

 

[Steve S]

I spent some time on the phone with Tesla yesterday on this issue. I'm leaving for a lengthy trip next week and was intending to take the Tesla. The nearest SC is 2.5 hours away, and in reality, it's 3+ hours away. Tesla said the apt would be 1.5-2 hours total, and the. I have to drive the same distance back. All over a 12V battery! A huge loss of productivity for sure.

I asked Tesla why they wouldn't just pick up the vehicle since its under warranty, and that if I just drove it until the battery went out, they would be picking it up anyways at their cost. They apologized that they couldn't. I had a similar warranty issue with a BMW years ago (alternator failed) and this was their grey area as well.

When I purchased this Tesla, my major concern was that I would be taken care of since I live in a smaller city surrounded by rural area (I have at least 4 other MS in my hood as well). That really isn't happening. Tesla needs to expand on SC's fiercly as when the M3 hits, there will certainly be issues like mine, but on a grand scale. We all know the media would be out to slay Tesla.

Anyways, looks like I will get some nice Chicago deep dish on Friday for lunch.

 

[DFibRL8R]

Well warm weather has arrived in Virginia and today I was greeted with the dreaded "12V battery needs service" warning. That's funny, I thought cold weather was when 12V batteries are supposed to have problems.

My original first generation 12V was replaced after 8 mos and about 15k miles. It's replacement has made it another 28mos and 56k miles...not bad given what I've been reading on this thread. Still, not looking forward to paying for this out of warranty "repair" which is something on every other vehicle I have owned was just a quick trip to the auto parts store and a 15 min swap-in. Given that I will be paying for this out of pocket and I generally like working on my cars, I would like to do it myself but there seems to be no good resources (you tube videos, manuals etc) on how to and a general consensus from those that have that it is a real PITA.

 

[Edmond]

I've looked into this, and I don't see why any deep discharge at 33Ah or better wouldn't do. I don't really trust Tesla's brand after all this, TBH.

There are several batteries that carry 35Ah, of about the same physical size, for less than $100. Mainly a question of adapting the terminals.
Amazon.com : 12V 35Ah Deep Cycle Solar Battery Also Replaces 33Ah 34Ah 36Ah - Mighty Max Battery brand product : Sports Outdoors
LifeLine 12V RV Deep Cycle 33ah AGM Battery - Batteries - Batteries Battery Supplies - Electrical
Sears.com
Sears.com
Sears.com
Sears.com

 

[Ingineer]

The C&D DCS-33IT battery Tesla is now using (red case) is a high quality AGM battery. They used to use these crappy grey ones.

I doubt you'll do better than the C&D unless you go with Lithium.

Also, if you're about to take a trip and you're worried about the 12v, just bring along a 12v jump-pack, then you won't be stranded. The Model S jumps just like an ICE car, all you need is to pop the nosecone off and there are 2 terminals right there. If your car is dead or won't close contactors, just apply an external 12v source to the jump posts and then step on the brake and it'll fire up.

The only thing that could leave you truly stranded is a DC-DC converter failure. If this happens, then the 12v system will stop getting power from the main (traction) battery and start draining the small 12v. This will quickly deplete it and the car will die. You will get a "pull over" message if this happens. The only way I could think of to avoid a tow at that point would be to buy a large 12v battery, such as the kind a semi uses and throw it in the frunk. Connect it to the jump posts and the car will start and drive as long as it holds out. Turn off all non-essential loads, such as climate control, lights, etc. Dim the screen all the way down.

Just back of the napkin calculations show that a 250 amp-hour truck battery should get you at least 6-8 hours of driving (single motor car) if you conserve 12v power.

The way the system works in the Model S is the 12v voltage is monitored when the car is asleep. If the 12v gets low, the car wakes up and closes it's main battery contactor to recharge the 12v battery. This in "Tesla speak" is called support mode. Once the 12v is topped off, the car goes back to sleep. This is where the "vampire" load comes from. If the car detects that it's entering support too often, or that it can't complete charging the 12v during support mode, you will get the alert message. (also the car will call Tesla and let them know too)

Not a catastrophe as long as there is at least a few % in the main pack, you will just see an increased vampire loss as support mode starts running longer and longer.

Very rarely is there a 12v battery failure without warning, catching the support mode off-guard. This can result in a "dead" car needing a jump.

Also, note, unless the DC-DC fails, the car will not "die" on the road as long as you keep it on. You can literally yank the 12v right out of the car and the car will keep going forever as long as you don't let it go to sleep.

 

[Lloyd]

So do you think my Dec 2013 car might have the newer one?

Will have to eventually get mine replaced anyway? Do I need to make sure it happens before my warranty expires.

Probably, My delivery was in July

 

[AB4EJ]

The C&D DCS-33IT battery Tesla is now using (red case) is a high quality AGM battery. They used to use these crappy grey ones.

I doubt you'll do better than the C&D unless you go with Lithium.

Also, if you're about to take a trip and you're worried about the 12v, just bring along a 12v jump-pack, then you won't be stranded. The Model S jumps just like an ICE car, all you need is to pop the nosecone off and there are 2 terminals right there. If your car is dead or won't close contactors, just apply an external 12v source to the jump posts and then step on the brake and it'll fire up.

The only thing that could leave you truly stranded is a DC-DC converter failure. If this happens, then the 12v system will stop getting power from the main (traction) battery and start draining the small 12v. This will quickly deplete it and the car will die. You will get a "pull over" message if this happens. The only way I could think of to avoid a tow at that point would be to buy a large 12v battery, such as the kind a semi uses and throw it in the frunk. Connect it to the jump posts and the car will start and drive as long as it holds out. Turn off all non-essential loads, such as climate control, lights, etc. Dim the screen all the way down.

Just back of the napkin calculations show that a 250 amp-hour truck battery should get you at least 6-8 hours of driving (single motor car) if you conserve 12v power.

The way the system works in the Model S is the 12v voltage is monitored when the car is asleep. If the 12v gets low, the car wakes up and closes it's main battery contactor to recharge the 12v battery. This in "Tesla speak" is called support mode. Once the 12v is topped off, the car goes back to sleep. This is where the "vampire" load comes from. If the car detects that it's entering support too often, or that it can't complete charging the 12v during support mode, you will get the alert message. (also the car will call Tesla and let them know too)

Not a catastrophe as long as there is at least a few % in the main pack, you will just see an increased vampire loss as support mode starts running longer and longer.

Very rarely is there a 12v battery failure without warning, catching the support mode off-guard. This can result in a "dead" car needing a jump.

Also, note, unless the DC-DC fails, the car will not "die" on the road as long as you keep it on. You can literally yank the 12v right out of the car and the car will keep going forever as long as you don't let it go to sleep.

Let's say you have to leave the car somewhere where you can't plug it in (say, at airport) for a couple of weeks.... has anyone experimented with disconnecting the 12v battery entirely for storage?

 

[Ingineer]

Let's say you have to leave the car somewhere where you can't plug it in (say, at airport) for a couple of weeks.... has anyone experimented with disconnecting the 12v battery entirely for storage?

This will definitely save wear and tear (charge cycles) on your 12v. Problem is it's tricky to do. There is no easy way to do it unless you add a battery disconnect switch in advance. You'd definitely need tools, and even so, hard to secure the car after there is no 12v, and if you close the frunk all the way, it's really hard on non-D cars to get it open without a jump.

Let me do some testing and see if there isn't a quick and dirty way to pull certain fuses that will effectively do this.

To be continued...

 

[CSFTN]

This will definitely save wear and tear (charge cycles) on your 12v. Problem is it's tricky to do. There is no easy way to do it unless you add a battery disconnect switch in advance. You'd definitely need tools, and even so, hard to secure the car after there is no 12v, and if you close the frunk all the way, it's really hard on non-D cars to get it open without a jump.

Let me do some testing and see if there isn't a quick and dirty way to pull certain fuses that will effectively do this.

To be continued...

I know the point I am about to make has been addressed before, but in light of what Ingineer is about to test .... If you're going to pull the battery, why wouldn't you just put a trickle charger on it? I know that we shouldn't need a trickle charger, as the traction battery should do that ... but either 1) it isn't or 2) it is, and the deep discharges that are happening kill the battery off in < 1 year anyway. If it is (#1), and the problem is deep discharges while driving, then taking out the battery shouldn't help, no? If the traction battery isn't adequately 'trickling' to the 12V (#2), then a trickle charge should work at least as well as removing the battery. No? The other question I can't help but ask ... if the Telsa stays plugged in when it is home, why is it that the car doesn't keep the 12V topped off completely? Is the process of 400V -> 12V inefficient, or does this type of battery get damaged by too frequent charging? And if the 400V -> 12V is inefficient, why can't it take the power from 120V of your electrical service to trickle the battery directly (like a trickle charger does?)

 

[ArtInCT]

I wonder just how many charge cycles the 12V battery can take AND I wonder what the watt draw is that the 12 volt battery is subjected to? Once those data points are known, then we can figure out what the output of a "trickle" charger needs to be. I wonder if it is more than a "trickle"?

Also the 12 volt battery is not thermally protected by the Tesla, when I had my fishing boat, the really cold weather was murder on the typical lead acid batteries. (4 deep cycle packs).