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

[santana338]

To everyone discussing getting a float charger - doesn't santana's data show the 12v recharge cycle being extended the same when plugged in as when on the float charger? This suggests that leaving the car plugged in effectively acts like having a float charger. It's only when he unplugged the car that you see the rapid discharge and frequent top offs on the 12v. I don't see any reason to get a float charger from his data.

"A plugged in Tesla is a happy Tesla." Perhaps this is one more reason why.

I believe it is true that a plugged in Tesla has the same effect on the 12V battery as a 900 mA float charger. As we know, this will result in the battery failing in about a year. The question is what will happen with a larger (4A or 8A) float charger on the battery? If this can prevent the discharge/recharge cycles then the battery should last much longer than a year. That is what we are assuming will happen but there is not data yet to show this is the case. If someone who has one of these chargers (Cottonwood maybe) wants to try this out I would be happy to loan him my data logger so we can see the results with a larger charger.

I don't plan to put a float charger in my car until Tesla stops replacing batteries annually. I remember reading (in this thread or another) that Tesla is aware of this problem and is working on a fix. So this is just investigating the problem to understand it so when the fix comes out it can be evaluated.

 

[neroden]

Thanks kennybobby! My math says that the peak current through each Model S contactor is 350kW / 350V = 1,000A. That's double the max current carrying rating of the contactor you linked, but the data sheet does provide some information on coil resistance, with which we can speculate about the current to hold the contacts closed. At 12V, the coil resistance is 11Ω, meaning 1.1A. That's 13.1W to keep it closed. With two relays in the Model S pack, one + and one -, that's 26W, or half of the roughly 50W average vampire drain! That's such a large number, it makes me question my contractors held closed theory, but it would explain a significant chuck of the vampire drain which is otherwise unexplained.

Hmmm. However, these should open when the car finishes charging. The vampire drain on a fully charged car should be:
(1) keyfob radio
(2) whichever computer is watching the keyfob radio
(3) pack temperature sensor
(4) whichever computer is watching that
Period. Nothing else needs to be on full-time.

 

[SteveS0353]

Hmmm. However, these should open when the car finishes charging. The vampire drain on a fully charged car should be:
(1) keyfob radio
(2) whichever computer is watching the keyfob radio
(3) pack temperature sensor
(4) whichever computer is watching that
Period. Nothing else needs to be on full-time.

plus 3G, WiFi and Bluetooth radios with the CPU taking care of wireless connections to the mothership, plus battery monitoring (12V and main pack), plus background processing (clock, etc). I still can't explain all of the large vampire drain, but there is clearly more going on in the background.

 

[aaronw]

I wonder if adding desulfate support to the battery charger would help? From my experience it can significantly extend the life of a battery. I periodically ran a desulfate cycle on one of my older cars with my battery charger and the battery lasted 10 years. I guess another solution would be to switch to another lithium battery, perhaps a lithium iron phosphate battery. So far I'm on my 3rd battery in a bit over 2 years.

 

[Matias]

plus 3G, WiFi and Bluetooth radios with the CPU taking care of wireless connections to the mothership, plus battery monitoring (12V and main pack), plus background processing (clock, etc). I still can't explain all of the large vampire drain, but there is clearly more going on in the background.

Vampire drain costs approximately 2 euros a day even if I'm not driving. It is a considerable cost on the long run. They really should address this better.

Edit: miscalculated by the factor of ten

 

[JRP3]

I I guess another solution would be to switch to another lithium battery, perhaps a lithium iron phosphate battery. So far I'm on my 3rd battery in a bit over 2 years.

Iron phosphate or lithium titanate. There is simply too much cycling going on for the lead acid battery. If they can't drop the the vampire load significantly then they need a more robust battery.

 

[mknox]

Iron phosphate or lithium titanate. There is simply too much cycling going on for the lead acid battery. If they can't drop the the vampire load significantly then they need a more robust battery.

Is it cycling or the amount of energy being drawn from the battery? Most modern cars have systems that constantly tap the 12v battery. Things like radio presets, OnStar telematics and such, and those 12v batteries will drain down if the ICE car isn't driven for a period of time. Not sure what makes Tesla "special" in this regard.

 

[spottyq]

Is it cycling or the amount of energy being drawn from the battery? Most modern cars have systems that constantly tap the 12v battery. Things like radio presets, OnStar telematics and such, and those 12v batteries will drain down if the ICE car isn't driven for a period of time. Not sure what makes Tesla "special" in this regard.

Tesla cycles* the 12V a few times a day (recharging it from the HV battery) whereas every other manufacturer manages keep the 12V sufficiently charged to crank an engine up after weeks without problems.

* I do not know the SOC window they use for the 12V battery. It is probably quite conservative, which would lead to cycling more often (but would reduce wear and tear on the 12V.)

 

[JRP3]

Is it cycling or the amount of energy being drawn from the battery?

They are directly related. More energy drawn from the battery = more cycling of the battery. I think it's something like a 30 amp hour battery and vampire drain is something close to 10 amps, so less than every 2 hours the battery is cycled since they can't let it go to 70% discharged, probably try to keep it above 50%.

 

[jbcarioca]

I recall several ICE cars i have owned that had similar issues if they were not driven every day. I had two Porsches (964 and 993) both of which required new batteries every nine months or so until i connected them to trickle chargers all the time when not driving. Ditto for an Alfa, three BMW's (M3, 535, Z1). It took me a very long time to finally connect all my ice to a trickle charger. All of them would sit unused for weeks/months at a time. With the S, I note that it can sit for two or three days while SOC drops 5-6% prior to triggering a main battery recharge when connected all the time. It stands to reason as several have mentioned that the continuous duty of the 12v probably places far more severe 12v duty cycles than is typical of any ICE. Very few ICE vehicles have a substantial load when the ICE is not operating. Our S's have air conditioning, BMS, communications, etc all running with no ICE producing continuous alternator feeding the battery. Regardless of how deep it cycles, the duty cycle is a tough load to bear.

Anybody want to wager that the Model X 12v system support might be a complete redesign? One could even imagine a more elegant solution being a dedicated 400v/12v inverter supplying all those loads directly from the main battery. That was the solution in a solar home I built almost 20 years ago. Such a solution could pretty easily be a retrofit for S's too. A side benefit just might be weight reduction, and logically it should be simpler than the current solution.

Looking out a couple of years: high end ICE cars are almost certain to go to 24v or even 48v within the next couple of years due to the extremely inefficient support of 12v system. thus far nobody much has done that because all the automotive gear is built to 12v. It has been too expensive to produce a/c, control systems, audio-video, driver support etc for 24v. Now that is ready to change. IT could easily be convenient to raise the voltage on all those systems when tesla is building 500,000 cars a year, BMW, MB, VW, Toyota, Nissan etc all building myriad EV's and PHEV's that need all these systems. So, as my previous paragraph, why not just move to 24v for everybody. Everyone must be ready for that now. Even low temperature cranking for the now ubiquitous common rail diesels would improve measurably. The infamous low RPM bolatage drops that alternators cannot cure entirely could also effectively be reduced or eliminated.

 

[MsElectric]

None of our ICE cars have needed 12V battery replacements earlier than 4-5 years.

 

[jbcarioca]

None of our ICE cars have needed 12V battery replacements earlier than 4-5 years.

Nor have mine if there were daily drivers. their problem comes with extended periods without being driven. My ICE in my permanent home is now 5 years old with original battery. It is driven eery day. None of my ICE driven less regularly have battery life beyond 18 months unless i connected them to trickle chargers. I wonder why it took me so many battery replacements to settle on that solution.

 

[mknox]

None of our ICE cars have needed 12V battery replacements earlier than 4-5 years.

That's about my average too, and I even have a 2007 Pontiac with just about 100,000 miles on it's original 12v battery (knock on wood!). My mother still drives her '87 Chrysler LeBaron, but does let it sit for weeks at a time. It's 12v will go flat about 4 times a year and I will have to run over to her condo with my charger. Her batteries last about 2 to 3 years. The first replacement I got for her about 15 years ago came with a full lifetime replacement guarantee. I think I've got at least 5 free replacements out of that deal so far!

 

[jerry33]

The VW TDI required a battery every year. What's worse is that it would fall without warning and couldn't be jumped because it was shorted out. Several tows were required.

 

[mknox]

The VW TDI required a battery every year. What's worse is that it would fall without warning and couldn't be jumped because it was shorted out. Several tows were required.

In my early years of driving, every 12v battery I had failed like this. Sometimes even when I was driving. I'd come to a red light, the headlights would dim way down, the car would stall and that was it. For years I assumed that's how these things failed and was surprised when I eventually had a car that just got "weak" and wouldn't hold a charge overnight, for instance, but was fine if you boosted it and went on your way.

 

[supratachophobia]

Anyone like to hear something ironic? After all the problems I have had and the 18 service visits to address them in 10 months and 29k miles, I've never had the 12v problem. I should be a case study.

 

[Cottonwood]

Is it cycling or the amount of energy being drawn from the battery? Most modern cars have systems that constantly tap the 12v battery. Things like radio presets, OnStar telematics and such, and those 12v batteries will drain down if the ICE car isn't driven for a period of time. Not sure what makes Tesla "special" in this regard.

The Tesla Vampire, that sucks the life out of the 12V batteries, drinks about 40 Watts or about 3.3 Amps from the 12V battery. Other modern cars with many "always on" devices draw more like 0.1 Amp or 1.2 Watts. Tesla just was not careful in their design of hardware with respect to low power consumption in the "off" state. That lack of attention created a very thirsty Vampire...when will a redesign put a stake through the Vampire's heart?

 

[spottyq]

The Tesla Vampire, that sucks the life out of the 12V batteries, drinks about 40 Watts or about 3.3 Amps from the 12V battery. Other modern cars with many "always on" devices draw more like 0.1 Amp or 1.2 Watts. Tesla just was not careful in their design of hardware with respect to low power consumption in the "off" state. That lack of attention created a very thirsty Vampire...when will a redesign put a stake through the Vampire's heart?

We should leave garlic in the car when it is off. Or perhaps permanently put some near the battery. That should help.

 

[jbcarioca]

We should leave garlic in the car when it is off. Or perhaps permanently put some near the battery. That should help.

Why didn't I think of that. I DO put garlic in my car but I take it out when i enter my garage. Obviously I am completely negligent; You'd think i never had been in Romania.

 

[MsElectric]

Does anyone think the seemingly high vampire drain of the main battery pack has to do with the inefficiency of the lead acid battery as it seems all the electrical consumers sip away from the lead acid battery and that's what gets topped off.