12v battery issue, Tesla unsatisfactory response

[AlanSubie4Life]

So I honestly suspect that maybe half the car's existent life is spent in sleep, while the other half is spent awake, per hour-by-hour basis.

Tesla says that 1% per day (0.955*0.01*76kWh = 725Wh) is normal for vampire drain.

We know that idle mode is over 100W; let's say it is 150W for the sake of argument - we know this is not far off based on the charging efficiency vs. charge rate curve. I've seen multiple people state about 7W-10W for sleep mode (by monitoring 12V battery current).

We know that many people can hit the typical less than 3 rated miles per day of vampire drain. So 725Wh per 24 hour period, or less.

You can piece these pieces together and come up with reasonable scenarios:

You can't have more than 5 hours of time in idle to come in under 725Wh. That puts an upper limit on idle time for a well-behaving car. The rest of the time, 19 hours or so, is spent in sleep. 19 hours * 7W = 133Wh.

This results in about 3 wake ups a day for people to top off the 12V. I've seen a lot of TeslaFi data suggesting that's a decent approximation for a typical day.

The formula is (roughly):

7W*(x) + 150W*(24-x) = Vampire Energy (per day)

Or, x = ( 3.6kWh - Vampire Energy ) / 143W hours per day sleeping.

So, I suspect most cars spend most of their time sleeping.

 

[FalconFour]

You can't have more than 5 hours of time in idle to come in under 725Wh. That puts an upper limit on idle time for a well-behaving car. The rest of the time, 19 hours or so, is spent in sleep. 19 hours * 7W = 133Wh.

You're pulling bad math out of your arse to try to prove a nonsense point. Bad math: that you use pure numbers as if the world is bleached and sterile. You just can't do that.

You've completely ignored charging, for starters (a huge amount of time that, the entire time, the car is "idle"), as well as all the time people spend in Sentry mode - AND the fact that Tesla's "1% per day" is while the car is completely unused sitting in a parking lot for days at a time... not while it's in active use. Sure, the thing might be asleep the entire time it's on a parking lot unused, but when the car is used for daily commuting (as mine - never a dull day), it's likely only sleeping less than half its existent life.

I'd throw all that math away and try to work backwards from real-world measurements, not theoreticals. (if only we could get some stats from Tezlab...)

 

[AlanSubie4Life]

You're pulling bad math out of your arse to try to prove a nonsense point. Bad math: that you use pure numbers as if the world is bleached and sterile. You just can't do that.

Ouch! That’s nice. Sadly you have only addressed a portion of my argument. You didn’t even address my other post.

I think my numbers are pretty conservative. Of course you are right about the idle mode when Sentry is on, or the car is being driven (a very small % of the car’s life)! But I think my 7W number is probably a bit on the low side.

Running Sentry Mode all the time is an EXCELLENT way to preserve your 12V, I would guess. But it comes at a (substantial) cost. Way more cost than the battery it saves in most areas. ($175/yr at 10 cents per kWh.). 120V charging is also an expensive (inefficient!) and effective way to reduce 12V use.

Would be interesting to see correlations to different user habits, for sure!

But if you want, cut my number by 30%. It STILL is higher than the typical use for an ICE car. Likely by over a factor of two.

Again, my claim is, fundamentally: the longevity of a 12V battery seems to depend on how much energy you draw from it, primarily. It of course also depends on *how* it is drawn to an extent. Deep discharges are bad for shallow cycle batteries, which are the topic here. But in neither case are we dealing with deep discharges. I would further contend that it probably does not hurt the battery much to draw 5% in two seconds (an overestimate of the starting draw for ICE - could probably crank an engine for 30-40 seconds with a healthy battery) vs. several hours (Tesla). They are designed to source a lot of current.

If you research lead-acid batteries I think you will find this to be the case.

So, not such a gentle existence for Tesla batteries, after all. This is perhaps borne out by the results - a factor of 2-3 times less life than that in a regular vehicle, it appears.

Cut that vampire drain to 1W though, and we’ll be doing a *LOT* better than ICE, I bet.

BTW as long as users know their average vampire drain per day, my formula accounts for Sentry use, to first order.

 

[EnrgyNDpndnce]

Its not "proving a negative", like Aliens don't exist. Its a simple question of data: What is the MTBF of the Tesla 12V battery? What is the proportion of successful Tesla jumps? I agree that all we seem to have is anecdotal data and that is not a good basis for conclusions...

But like aliens and Mulder, The truth is out there... certainly Tesla knows and knows precisely what the demands are on the 12V battery and how it is being used relative to its optimal load and duty cycles.

You get an automatic “Like” for referencing Fox Mulder, one of the greatest TV characters ever!

And I agree that Tesla likely has the data we’d all like to see, and would love to see them publish it. Not gonna hold my breath, but I’d love to see it happen.

 

[EnrgyNDpndnce]

I was not talking about OEM

Did you find a deep cycle replacement ?

Bought an AGM that fits. I believe it was this one but I’d have to go look in my car to be certain, and I’m far too lazy to do that right now.

 

[AlanSubie4Life]

Bought an AGM that fits. I believe it was this one but I’d have to go look in my car to be certain, and I’m far too lazy to do that right now.

What did you do about the vent hose? Since this is AGM I guess it doesn’t need it (???), but isn’t there one on the OEM battery in case of an overpressure event?

 

[beachsideev]

agm batteries aren't vented and can be installed in any orientation.

if the oem battery has a vent, it isn't agm.

 

[brkaus]

Don’t AGM have a slightly different charging profile vs standard lead acid?

 

[AlanSubie4Life]

if the oem battery has a vent, it isn't agm.

Yeah that is what I thought. Thanks.

 

[SageBrush]

I believe it was this one

That battery is not labeled 'deep cycle' but I do not know what that translates into by spec.
The good news is that it is a recommended replacement for Toyota highlander hybrids, so that is something.

Addendum: From howstuffworks.com

A car battery typically has two ratings:

• CCA (Cold Cranking Amps) - The number of amps that the battery can produce at 32 degrees F (0 degrees C) for 30 seconds
• RC (Reserve Capacity) - The number of minutes that the battery can deliver 25 amps while keeping its voltage above 10.5 volts

Typically, a deep cycle battery will have two or three times the RC of a car battery, but will deliver one-half or three-quarters the CCAs. In addition, a deep cycle battery can withstand several hundred total discharge/recharge cycles, while a car battery is not designed to be totally discharged.

I found this optima battery labeled for deep cycle use that has less reserve capacity than the battery you bought. So either the Optima is crap, or you made a good choice

 

[AlanSubie4Life]

That battery is not labeled 'deep cycle' but I do not know what that translates into by spec.
The good news is that it is a recommended replacement for Toyota highlander hybrids, so that is something.

Unfortunately it's 60% more expensive than the OEM battery (which is not AGM, according to all the signs (manufacturer document, presence of a vent tube, cost)). It's probably fine, of course, and it might even last longer - as long as the charging profile for the AGM is the same as it is for an SLA (my understanding is that they are not). Perhaps the charging profile won't matter much - no idea. All I know is that AGMs are treated slightly differently and if the car doesn't know this, I am not sure what the impact will be on longevity. It obviously would depend on the degree of mismatch.

I'm not sure why anyone who is *not in an emergency situation* would spend $190 on a battery, when the (cheap) replacement 12V will be covered under warranty.

Of course, here I am, unable to make a service appointment in the app, or contact Tesla at all, and I suspect my battery is nearing expiration. So I guess I see how things work out in real life. I guess if I were smart I would pick up a battery from Autozone or O'Reilly's just to keep it in reserve.

 

[SageBrush]

I think this battery has the PbA specs we want, although I have not verified that the orientation and posts are correct

Duracell Ultra Platinum AGM BCI Group S46B24R Car and Truck Battery - SLI51PAGM at Batteries Plus Bulbs

Please let me know if I am barking up the wrong electrode

 

[SageBrush]

I'm not sure why anyone who is *not in an emergency situation* would spend $190 on a battery, when the (cheap) replacement 12V will be covered under warranty.

Of course, here I am, unable to make a service appointment in the app, or contact Tesla at all, and I suspect my battery is nearing expiration. So I guess I see how things work out in real life. I guess if I were smart I would pick up a battery from Autozone or O'Reilly's just to keep it in reserve.

If I lived within driving distance of a Tesla service center, that would be my default choice to buy one there and install myself without an appointment

 

[AlanSubie4Life]

If I lived within driving distance of a Tesla service center, that would be my default choice to buy one there and install myself without an appointment

I live within driving distance, but frankly was just hoping for mobile service, so I don't have to undo the rear seat, undo the DC-DC connector, etc., following the recommended procedure in the FSM (which I have to guess at unfortunately). Obviously I could do it (and I may have to since I can't contact service through the app), but the risk is slightly elevated. Sadly they don't have 12V replacement on the do-it-yourself list.

Also this would mean I would likely have to pay for the battery, which is not really that big a deal, but it's also not really right. I'm fairly sure mine is bad so I need them to look at it remotely - it would of course be covered under warranty. But sadly the app is non-functional when it comes to Service.

 

[AlanSubie4Life]

I think this battery has the PbA specs we want, although I have not verified that the orientation and posts are correct

Duracell Ultra Platinum AGM BCI Group S46B24R Car and Truck Battery - SLI51PAGM at Batteries Plus Bulbs

Please let me know if I am barking up the wrong electrode

Just make sure the electrode orientation and size are correct. This doesn't look quite correct (these are pencil posts (P) and I don't think that is correct. The Tesla Model 3 uses a 51R, so your electrodes are also in the wrong place, but it may be ok if there is enough slack on the cables. Pencil posts are a hard no though) but I'm not an expert on this, as I'm not interested in replacing an SLA with an AGM (the profiles are different so the AGM may be damaged - not sure how big a problem it is). I think someone posted other matches earlier in this thread, but don't know how many were AGM and how many were SLA. Get the cheaper one (SLA), probably.

Posted earlier; last one in the list; you want SAE posts:

 

[EnrgyNDpndnce]

What did you do about the vent hose? Since this is AGM I guess it doesn’t need it (???), but isn’t there one on the OEM battery in case of an overpressure event?

Interesting. I didn’t know what the vent hose was for, but the new battery had a place for it so I popped it on in the same way I took it off the OEM part. Orientation was the same.

 

[AlanSubie4Life]

Interesting. I didn’t know what the vent hose was for, but the new battery had a place for it so I popped it on in the same way I took it off the OEM part. Orientation was the same.

Interesting. I couldn't tell from your picture that there was a vent tube on the battery you got. It didn't look like it. Some people claim AGM don't need it. Seems to me maybe they do? They're for overpressure situations, and even if the electrolyte doesn't spill in an AGM maybe it still could have a vent (it pops open with overpressure I guess)? I really have no idea. Sounds like if yours is an AGM, then indeed AGMs sometimes have vent tubes.

 

[EnrgyNDpndnce]

So either the Optima is crap, or you made a good choice

Time will tell. Perhaps I just got lucky. Even a broken clock is right twice a day! (Those of you under 30 are probably scratching your heads right now)

 

[SageBrush]

Interesting. I didn’t know what the vent hose was for, but the new battery had a place for it so I popped it on in the same way I took it off the OEM part. Orientation was the same.

Doesn't that mean the battery you bought is not an AGM ?

 

[SageBrush]

Don’t AGM have a slightly different charging profile vs standard lead acid?

Some reading on the internet says that AGM charge at a lower voltage and can be damaged by typical charging voltages.

Nothing is simple anymore.

It is times like these that I wish Tesla sold repair manuals