12v battery issue, Tesla unsatisfactory response

[SageBrush]

I am not sure why that is needed.

That extra step is to disconnect a DC/DC converter.

If I understand correctly, failure to disconnect would be ~ the same as replacing the 12v on an ICE while the engine is running. Personally, I prefer extra safety steps because I am fairly ignorant about electricity so in addition to disconnecting the DC/DC I put the 12v battery terminals I take off the battery in plastic baggies.

 

[P3dStealth]

That extra step is to disconnect a DC/DC converter.

If I understand correctly, failure to disconnect would be ~ the same as replacing the 12v on an ICE while the engine is running. Personally, I prefer extra safety steps because I am fairly ignorant about electricity so in addition to disconnecting the DC/DC I put the 12v battery terminals I take off the battery in plastic baggies.

I get what you are saying. You are right. Maybe it's some kind of safety thing or maybe it just keeps the computer from throwing error codes. I pulled that plug off before it comes off easy anyway. Might as well do it.

Bad example though. Nothing happens on an ice if you disconnect and reconnect the 12v while it's running. It's an old trick to see if the problem is the battery or the alternator. You jump start the car and while it's running disconnect the battery. If the car starts turning off put the terminal back on and if it runs it's the alternator going bad not the battery.

 

[SageBrush]

Bad example though. Nothing happens on an ice if you disconnect and reconnect the 12v while it's running. It's an old trick to see if the problem is the battery or the alternator. You jump start the car and while it's running disconnect the battery. If the car starts turning off put the terminal back on and if it runs it's the alternator going bad not the battery.

That is the point -- you risk getting shocked by the hot terminal

 

[RayK]

Nothing happens on an ice if you disconnect and reconnect the 12v while it's running. It's an old trick to see if the problem is the battery or the alternator. You jump start the car and while it's running disconnect the battery. If the car starts turning off put the terminal back on and if it runs it's the alternator going bad not the battery.

You know the typical reason why one would jump a 12V battery, right? It's like what happened to the Dread Pirate Roberts after being in the Pit of Despair: it's mostly dead. So you find a friendly person with a car, jump your battery and while you got your car running and the alternator is charging the now partially dead 12V battery, you pull off one of the battery terminals and see if your car continues to run or stumbles to a halt.

Yes, in the old days this test might have worked. However, with today's systems you may have blown the regulator inside the alternator. Oh yeah, since the battery was mostly dead it's now in a charging state so that means current is flowing into the battery. When you interrupt this connection by pulling off one of the leads, negative is what was usually recommended I believe, there's probably going to be a spark. What's usually nearby a charging lead-acid battery? Oh, this image comes to mind:

So, no, I would not recommend pulling off either one of the battery leads when the engine is running.

 

[Sans-gas]

I was passenger in a Prius twice (same Prius) when the 12V died. No warning, nada. The second time it was really conveniently outside a battery store! I wouldn’t expect my Tesla to do any better.

I often drive alone. I hate depending on tow trucks, AAA etc, but in the back of my mind I’ve considered what my action might be if my pretty new Tesla died out in the sticks somewhere.

My action was to print the portion of the manual on how to open the compartment to tow and access the 12V battery and put it in an envelope in my console. I plan to replace it before 3 years. I would also recommend this for Prius drivers.

 

[P3dStealth]

You know the typical reason why one would jump a 12V battery, right? It's like what happened to the Dread Pirate Roberts after being in the Pit of Despair: it's mostly dead. So you find a friendly person with a car, jump your battery and while you got your car running and the alternator is charging the now partially dead 12V battery, you pull off one of the battery terminals and see if your car continues to run or stumbles to a halt.

Yes, in the old days this test might have worked. However, with today's systems you may have blown the regulator inside the alternator. Oh yeah, since the battery was mostly dead it's now in a charging state so that means current is flowing into the battery. When you interrupt this connection by pulling off one of the leads, negative is what was usually recommended I believe, there's probably going to be a spark. What's usually nearby a charging lead-acid battery? Oh, this image comes to mind:

View attachment 592331

So, no, I would not recommend pulling off either one of the battery leads when the engine is running.

Ha! I like the post but I was a mechanic for 8 years I must be lucky I didnt explode.

I give up.

 

[Daniel in SD]

Has anyone ever been injured from a hydrogen explosion from a lead acid battery?

Ha! I like the post but I was a mechanic for 8 years I must be lucky I didnt explode.

I give up.

62 of the 97 people on the Hindenburg survived so the odds were in your favor.
Seriously though has anyone ever been injured by a hydrogen explosion from a lead acid car battery? Seems so unlikely.

 

[RayK]

Google links to several, what I would consider reliable, sites where they describe the occurrence of battery explosions. Some are old (circa 1990's), while others are within the last 10 years. Most newer references describe Li-ion batteries as that's the public's awareness nowadays. While not involving a car battery, this article does highlight some dangers: Exploding lead acid batteries | Business Queensland

And this was from about a year and a half ago in Montana: Lesson Learned: Exploding Batteries

Basically, I think no matter what the application, purposely or knowingly generating a spark around a lead-acid battery, especially if it's being charged, is kind of like drawing a raffle ticket to a Darwin Award. It's not a good idea to do it. Sure you can play the odds and say 999 times out of 1,000 nothing will happen but do you want to be that 0.1%?

Ooo... here's a good one: https://www.nfpa.org/-/media/Files/...rts/Hazardous-materials/RFLeadAcidBattery.pdf

 

[Daniel in SD]

Google links to several, what I would consider reliable, sites where they describe the occurrence of battery explosions. Some are old (circa 1990's), while others are within the last 10 years. Most newer references describe Li-ion batteries as that's the public's awareness nowadays. While not involving a car battery, this article does highlight some dangers: Exploding lead acid batteries | Business Queensland

And this was from about a year and a half ago in Montana: Lesson Learned: Exploding Batteries

Basically, I think no matter what the application, purposely or knowingly generating a spark around a lead-acid battery, especially if it's being charged, is kind of like drawing a raffle ticket to a Darwin Award. It's not a good idea to do it. Sure you can play the odds and say 999 times out of 1,000 nothing will happen but do you want to be that 0.1%?

Ooo... here's a good one: https://www.nfpa.org/-/media/Files/...rts/Hazardous-materials/RFLeadAcidBattery.pdf

Don't get me wrong I always connect to chassis ground when jump starting a car. That article does conclude that lead acid batteries have low fire risk. I admit that I didn't realize that the concern was an explosion inside the battery. I thought it was just the possibility of singed eyebrows from a hydrogen explosion, not a face full of sulfuric acid!

 

[scottf200]

That extra step is to disconnect a DC/DC converter.

If I understand correctly, failure to disconnect would be ~ the same as replacing the 12v on an ICE while the engine is running. Personally, I prefer extra safety steps because I am fairly ignorant about electricity so in addition to disconnecting the DC/DC I put the 12v battery terminals I take off the battery in plastic baggies.

Similar disconnect requirement in the Service Manual for the Model X when changing the 12v battery. I did the disconnect recently to also shut down all the subsystems since Power Off menu option does not do that. I needed to restart the 'GPS' system.

 

[SageBrush]

This post is to clarify what I wrote earlier. Please correct as needed

In an ICE vehicle that is off, once the (+) terminal of the 12v battery is disconnected it is presumed to be unenergized. If the ICE is running, the alternator energizes the (+) lead to the 12v battery

In an EV with a 12v battery, the (+) lead may be energized by the traction battery via a DC/DC converter. Disconnect of the converter is analogous to shutting down the engine (and therefore the alternator) in an ICE vehicle.

---
Engineers may do differently, but normal folk should be handling unenergized wires.

 

[scottf200]

My prev post: 12v battery issue, Tesla horrific response

Yeah, that's the one. I bought one from AEG but it uses the same app and is essentially the same device. Easy to setup with the exception that the positive lead on the 12v is a little tricky to connect the clip and then put the red rubber cap/seal back. I bent the clip in an L shape and managed and also used some waterproof electrical tape to make sure it would stay in place.

I just finished the install and it is working well. The yellow line shows were I used some wire cutters to notch out a 1/8" x 1/2" section so the red cap would fit perfectly. I also pinched the 'U' top legs together a little so it would fit nicer under the nuts.

ScanMyTesla shows my DC-DC converter actively working with the numbers changing constantly.

I'm trying to monitor how my 12v battery is doing as a test when I run my 12v fridge. So far in all the testing with my fridge on for 1+ hrs, my voltage has been very steady at 13.19v to 13.24v and typically 13.21v.

 

[SageBrush]

@scottf200,
I was also looking at SMT this morning and saw the active DC/DC converter. I powered off the car but the converter stayed active for the couple of minutes I monitored it.

As an aside, I decided to annually monitor the 12v capacity, OCV after rest, and internal resistance (AC 1 kHz test) rather than blindly replacing the 12v on a (perhaps too) frequent basis. I don't have baseline readings from when the 12v is new, so do you or others have ballpark figures that suggest replacement in the near future ?

 

[scottf200]

@scottf200,
I was also looking at SMT this morning and saw the active DC/DC converter. I powered off the car but the converter stayed active for the couple of minutes I monitored it.

As an aside, I decided to annually monitor the 12v capacity, OCV after rest, and internal resistance (AC 1 kHz test) rather than blindly replacing the 12v on a (perhaps too) frequent basis. I don't have baseline readings from when the 12v is new, so do you or others have ballpark figures that suggest replacement in the near future ?

I have an X so my experiences are certainly different. My X doesn't go into sleep and I use a 12v fridge when going on bike rides or constantly when on roadtrips. I figured it would be harsher on the battery. Monitoring the 12v directly using this hardware is not showing near the voltage change I expected. I used SMT to gather 12v data for my graph in this post which showed a lot of differences at different duty cycles: Annotated Fridge/Freezer that fits the Model X is on sale and initial same graph: Fridge/Freezer that fits the Model X is on sale

It seems like ideal we would have monitored our batteries when new. I only recently got into looking at the 12v since I have a 2017 (bought used as a service loaner) and like roadtrips so I'm worried about my battery dying while on a road trip. Curious about how you are doing the open-circuit voltage (OCV)? Are you disconnecting the 12v post and just letting the battery sit for some number of hours?

I tested my IR again since I had my frunk tore apart again to get at the 12v.

 

[SageBrush]

Curious about how you are doing the open-circuit voltage (OCV)? Are you disconnecting the 12v post and just letting the battery sit for some number of hours?

Yep. First test is pending; I planned on 3-4 hours disconnected before testing OCV

In addition to an AC IR tester, I am going to buy something like this to test capacity. My plan is to

1. Trickle charge to full with terminals disconnected
2. Discharge to ~ 3v with a 12v, 15watt bulb (under 3 hour discharge)
3. Note capacity

I think I'll swap when capacity is ~ 70% of new, or if the other tests are way out of whack

Sound reasonable ?
Dumb question: I presume the electronic doodad and light bulb are in parallel, right ?

 

[scottf200]

Yep. First test is pending; I planned on 3-4 hours disconnected before testing OCV

In addition to an AC IR tester, I am going to buy something like this to test capacity. My plan is to

1. Trickle charge to full with terminals disconnected
2. Discharge to ~ 3v with a 12v, 15watt bulb (under 3 hour discharge)
3. Note capacity

I think I'll swap when capacity is ~ 70% of new, or if the other tests are way out of whack

Sound reasonable ?
Dumb question: I presume the electronic doodad and light bulb are in parallel, right ?

I haven't read much about the discharging method to test the capacity of a 12v car battery. There are also supposed to be smart battery charger (noco, ctek, etc) that some say extend the life but I wonder how sophisticated Tesla's method (DC-DC when not driving) is after years of tweaking.

That tester you pointed to doesn't seem like it is for AGM lead-acid batteries. You can see the model/brand I'm using which has a test option for a battery that is in or out (OC) of the car. The directions for it have you remove the 'surface charge' by running your headlights (also stated in article below).

The Battery University article talks about removing 1% of the 'surface charge' for testing.

Water Loss, Acid Stratification and Surface Charge - Battery University
Surface Charge __ Lead acid batteries are sluggish and cannot convert lead sulfate to lead and lead dioxide quickly during charge. This delayed action causes most of the charge activities to occur on the plate surfaces, resulting in an elevated state-of-charge (SoC) on the outside.
__ A battery with surface charge has a slightly elevated voltage and gives a false voltage-based SoC reading. To normalize the condition, switch on electrical loads to remove about 1 percent of the battery’s capacity or allow the battery to rest for a few hours. Turning on the headlights for a few minutes will do this. Surface charge is not a battery defect but a reversible condition.

If I were running your test I would run the lightbulb and "QUICKLYNKS-Battery-Monitor-Bluetooth-Device" in parallel for sure.

Battery Univerity article on measuring IR: How to Measure Internal Resistance

 

[AlanSubie4Life]

The Tesla battery is an AGM, deep cycle battery.

In Model 3 (other vehicles may be different!) we don’t know this to be true, AFAIK. The battery manufacturer’s document suggests it is not AGM (see above). MF type.

Circumstantial evidence: Tesla charged someone only $120 to replace the battery out of warranty (see above). That is too cheap for a small AGM battery as far as I can tell.

Anyway, one of these days we will find out whether or not it is AGM, with some sort of proof. My current bet is it is not AGM in Model 3.

 

[android04]

In Model 3 (other vehicles may be different!) we don’t know this to be true, AFAIK. The battery manufacturer’s document suggests it is not AGM (see above). MF type.

Circumstantial evidence: Tesla charged someone only $120 to replace the battery out of warranty (see above). That is too cheap for a small AGM battery as far as I can tell.

Anyway, one of these days we will find out whether or not it is AGM, with some sort of proof. My current bet is it is not AGM in Model 3.

If my OEM battery dies outside of warranty (2000 miles to go) I'll probably dissect the top of it to know for sure whether it's AGM or not. I expect it will be fine for a few more years though.

 

[smatthew]

If it knew the battery was low wouldn't it just charge it continuously.

If the battery shorts out (which seems to be a common failure mode) it starts drawing large amounts of power. The car notices this, says "Something's wrong" and stops charging. Then the car dies. If it kept charging the battery things would get worse.

in an ICE car, usually a car needs to be jumped because something drained the battery while the car was off. It usually causes damage to the battery, but you can re-charge the battery and keep on using it for a while usually. That's what battery maintainers are for. Some Leaf owners had to plug battery maintainers in because their car wasn't keeping the 12V charged properly.

In a Tesla, the 12V battery is maintained by the DC/DC converter, so it never gets accidentally drained. What happens is the battery fails, shorts out a cell, and really dies.

 

[Skione65]

To anyone running the Ancel or Quicklinks Battery Monitor (@webbah @scottf200 and @Watts_Up ) have you noticed inaccuracies in the Voltage percentages from reality (I.e. side by side testing with a voltmeter and what you get with the app)? Was going to pull the trigger on one however there were numerous reviews on both with reviewers posting photos of the side by sides and there were big differences. In essence they (and I) were saying what’s the point if (a) the voltage percentages are not within the variance tolerance spec the manufacturers list and (b) quite often the monitor would list a trigger for a low voltage warning and the owner would voltage test with an actual meter and it would be fine? (I.e. the Voltage output indicated thus triggering a warning would be way less than actual voltage in reality after a vmeter test).

Any input appreciated. Really would like this unit but want it to be accurate...as I have a enough to worry about without constant false readings. After all I’m purchasing to alert me to “pre-failure” of the 12V so I don’t get stranded.

Also is a power draw oh 1 mA - 1.5mA enough to slowly drain the 12V when parked let’s say for 4 days and NOT plugged in and charging?


Regards,

Ski