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Rate of discharge when parked -- conflicting info?

Back in February, we had an "infamous" blog post from Tesla declaring that:

For example, a Model S battery parked with 50 percent charge would approach full discharge only after about 12 months.

Yet the owner's manual states (page 25):

On average, the Battery discharges at a rate of 1% per day.
...
For example, over a two-week period (14 days), the Battery discharges by approximately 14%.
...
To protect against a complete discharge, the Model S enters a low-power consumption mode when the charge level drops to 5%. In this mode, the Battery stops supporting the onboard electronics to slow the discharge rate to approximately 4% per month. Once this low-power consumption mode
is active, it’s important to plug in the Model S within two months to avoid Battery damage.

So according to those figures in the owner's manual, if you park with 50 percent charge, then you'll enter low-power mode in 45 days and risk damaging the battery after just over a month from that point. Overall, this means that it takes less than 3 months to completely discharge the battery, after parking at 50%.

That's a far cry from the blog post's claim of 12 months. Any thoughts? Maybe there's a typo in the owner's manual for the discharge rates?

Do we know whether the 1% per day figure is based on a fully charged battery or on the amount of charge remaining in the battery? In other words, if the battery is fully charged (85 kwh), it presumably discharges at approximately 0.85 kwh per day. However, when it is 50% charged (42.5 kwh) does it continue to discharge at .85 kwh per day, or does the discharge rate slow down to .425 kwh per day? I understand that if the latter case were true, the battery would never discharge completely. However, do we know whether the discharge rate is linear or non-linear?

@DouglasR - good points! I know (from engineering some hand-held products) that nothing is linear about Lithium battery performance! They are amazingly complex devices to characterize which is what makes 'battery percent' display so complex to make accurate.

Your theory makes sense to me as self-discharge is a function of cell voltage so that will slow as discharge occurs. As posted by others that is why cell manufacturers suggest charging to 70% before placing cells (or products) in storage to maximize battery life.

I wonder how many people this is an issue for? If you're parking it for a long time at home you're plugged in and in "storage" mode, so no issue. If not at home you may not have your 240v outlet available but I bet you have a 120v outlet. I'm trying to think of a scenario where someone would leave the car sitting unplugged for so long that it's a problem.

After 12 months idle, even an ICE car can brick, as the oil eventually will start to solidify, unless it is run periodically (nevermind what can happen to gasoline after that length of time).

Besides, who would leave a $65k to $110k Model S not pluged in for three months? Well, maybe someone in an area where it takes months to fix the power after a natural disaster. Otherwise, I can't think of any other reason?

Either way, the Model S (much less any EV) is going to require some new ways of thinking when it comes to maintaining it. I for one am more than happy to take on these new ways of 'thinking'.

I have been camping more than a month in a place where you didn't have any electricity available. I can easily think some scenarios where people camp even longer times in such places.

I have vague memory about some Tesla text that says that discharge slows down a lot when battery gets closer to full discharge. Discharging was fastest when battery was full.

The 1% per one day is clearly stated as a rule of thumb. As such, and because the issue is so important, it is only to be expected that it includes a safety margin of an order of magnitude.

Timo | SEPTEMBER 26, 2012 NEW
I have been camping more than a month in a place where you didn't have any electricity available. I can easily think some scenarios where people camp even longer times in such places.

Then I highly recommend you don't take your Model S on any of these trips. You probably also want to avoid taking it through water over 3 feet deep, off-road through mud or over terrain suitable for mountain bikes or mountain goats. I believe the Model S is also not appropriate for use as a flotation device in white-water rafting excursions. If going into combat areas, please also be aware that it is not bullet-proof or land mine resistant in any way.

@ tesla.mrspaghet
+1

LMBFUAO(Big Fat Uncivilized)

@tesla.mrspaghet +XX
Enjoying a great laugh!!!

But Timo has a good point, I think quit a few of the model S owners can enjoy lengthy time off like Timo mentioned. +X

Thank you, thank you, I'm here all week... :)

Not begrudging anyone lengthy time off, but the point is that it will be plugged in during any such vacations/safaris/climbing trips to Kilimanjaro, etc.

You guys are very funny and entertaining. If the amount of time you spend on TM Forum is an indication, you will be driving your “…Ss off!” Tour BEV will only sit still while it is charging/recharging.

Tikiman. Gasoline does degrade but it often takes many years for it to crystallize or go foul. Also, I suspect once you get your “S” we will not be hearing from you. You strike me as being the type that would prefer to drive the drive rather than talk the talk.

Timo. My son says he will switch his 2010 Toyota FJ (4x4) for your “S” when you are off for a month+ being one with nature.

Sorry "Your BEV..." not Tour!

The point isn't that the time implied by the manual's description is too short. The point is that (precisely as stated) the manual conflicts with prior statements made in a highly-publicized blog entry. And that those statements were made specifically to address rumors that the battery could fully discharge quickly/easily. I was extremely impressed when that blog entry came out... a year is a long time for a 50% charge to take to dissipate!

So let's assume exponential decay of charge, instead of linear. In that case, the current charge (before low-power mode) is 0.5 * 0.99^n where n is the number of days. Using that formula, we would drop below 5% state of charge starting on day 230. That's 7.5 months of time.

At that point we're in the low-power consumption mode. The manual also says:

Once this low-power consumption mode is active, it’s important to plug in the Model S within two months to avoid Battery damage.

Which brings us to 9.5 months total, from parking at 50% SOC to battery damage.

That's getting *much* closer to the blog entry's statements. Close enough that the delta is easily explained by more precise models of the battery's discharge rate than a simplistic "exactly 1% per day."

Don't forget the Battery TMS is supposed to kick in, if the ambient temperature is high. So in hot areas (US Southwest), the battery may not even last a month from full charge when unplugged.

Everything goes bad faster in the heat. It's a Law of Nachure.

The skew between blog post and manual is based on the nature of each document.

The manual has the burden of being very conservative to encourage the owner to protect the asset, and to define limits of company liability.

The actual self-discharge figures are much better than the manual suggests. Remember that initially the car is actually running equipment like network links and computers while it sits there. That's where the 1% a day number mostly comes from. They also have to allow margin for unfavorable enviromnental temperature in their guidelines. The point at which it switches to deep sleep mode is a firmware choice that TM can change in online updates, or even let you decide from the screen menu if necessary.

We manufacture stuff with lithium polymer cells. We once had 10,000 cells sit on the shelf for a year. The actual measured discharge on these cells was on the order of 15% in 12 months. This was due to the actual intrinsic self-discharge, and some modest warehouse temp cycling.

Because an EV battery is an high-value asset, TM has an obligation to advise with an abundance of caution.

Just follow the guidelines and leave it plugged in when you're gone. No big deal. Your ICE car lead-acid starter battery will die about 5-10 times faster, but in practice, that's not an issue either.

+1 Mark K
Thang kew!

OK all of these cold weather discharge postings are interesting, however, I would really like to understand how to turn of the computers and networking devices off if I intend to leave the vehicle parked for an extended period of time.

I live in South Florida so cold weather is not an issue. I often leave my Model S parked at the airport when I travel. Most recently I started paying attention to the difference in range when I park and return. The most recent trip was only for less than two days. When I left the car it showed 240 mile range remaining. When I returned approximately 40 hours later the range showed 219 miles remaining.

That is an 8%+ discharge over less that two days or approximately 4%+ per day. There must be a setting I am unaware of to make sure the car is using a minimal amount of power while parked or there is a problem with the vehicle. At that rate, if I left the car parked for 10 days with a 100 mile range remaining, unplugged at airport parking because there are no charging stations, I would likely have a dead battery when I return.

Absolutely love the car but this is an issue that needs to be clearly explained by Tesla. Any comments or advice from other Model S owners with similar issues would be appreciated.

Also, does anyone know when the APPS to interface with the car from your mobile device will be released?

@seanoday - what you want is sleep mode, which was removed in 4.2 and will be added back some day. Until then, you can't shut off the computers without pulling fuses, which would be a very bad idea.

The battery will not discharge to "dead"; it goes into a deep sleep mode (forget the exact charge level when this happens). TM has said the car will survive a 6 mo. abandonment. It may not be immediately drivable, but it will not be bricked/harmed.

I live in Central Florida. My car has lost 10 miles of range after having "completed charge" up to 241 miles. The loss of the 10 miles happened over the last 24hrs while still being plugged in to the 120 volt socket. I guess that is slightly more than 4% even still being plugged in. Is this normal? Temperature has been in the seventies.

Pablodds,

I would ask Tesla about it. It seems like a too high rate of discharge if the car is plugged in.

pablodds - totally normal. My Tesla loses about 12 miles during a 24 hour period even if plugged in (I live in AZ, so no issues with cold weather). The car will ultimately top off the charge but not until a certain threshold has been reached. Until Tesla reinstates deep sleep mode our cars will continue to behave this way. Not a big deal for me - but if you need the 241 miles - just switch over to max range for 30 minutes and the car will top off the charge. Just don;t let it finish charging all the way - not good for the battery.

Sunnysailor,

I will contact Tesla too see what they say about this.

Carefree

It's interesting to see your experience is the same as mine. I do wonder; if this is the normal behavior then why does the owners manual indicate a 1% loss over 24hrs should be the expected loss. I just want to make sure that there is not something about our car settings or something else I'm doing to cause this. Could it be possible that if the car were unplugged, the energy usage would automatically go into a more efficient mode and meet the 1% loss. I agree with you as far as it not being a big deal; to me it's not either, based on my current range needs.

Thanks for the feedback

@pablodds: Just to be clear. It's totally normal now, in that it's a known problem and there's nothing wrong with your particular settings or car. However, it's definitely an issue, and the actual loss is much more than the 1% in the manual. Tesla is working to fix the problem, and definitely will in an upcoming software update.

@gregv64,

Ok. It is good to hear that. I guess then we should just wait and see.

I have been telling the car to ignore the 4.2 install for over a month now because I didn't want to lose the sleep mode. Wasn't having any of the problems being reported with 4.1 that 4.2 was supposed to fix. I have confirmed on multiple occasions that I am only losing 2 miles of rated range per 24 hrs. Tesla really needs to get the sleep mode back on.

FWIW, I have tested my unplugged daily drain at several SOCs. I lose about 12-13 miles a day whether it had 240, 100, or 50 miles rated in the battery. So it seems to me the drain that it uses is the same each day, its just how much power it needs for the systems. My testing is done with car in the garage, between 50-60 degrees inside.


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