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How much will not charging every night hurt battery longevity?

I reserved a Model S on 1/23 and already got the Finalize button (that was fast!), but I'm having a hard time deciding if owning the Model S is going to be practical for me.

I currently rent an apartment in downtown Austin and have no plans of buying a house soon. My building does not have any charging stations, but there are several within a couple blocks of my apartment. I only commute about 10 miles roundtrip each day, so I was thinking that I could charge overnight once a week at one of the stations near me and be fine.

However, after doing more research, I found this on http://www.teslamotors.com/models/facts:

Battery lifetime is affected by both age and the total amount of energy it delivers over time. The Tesla battery is optimized for nightly charging: topping off frequently enhances the longevity of your battery.

So, now I am wondering if not charging every night is a realistic plan. Is it possible to only charge once every 3-5 days or less without hurting the battery? Will this significantly decrease the battery longevity?

I'm sure others who live in the city are struggling with similar problems. There are only 3 or 4 apartment buildings in Austin with charging stations. All of them are high end luxury apartments. While I'm already paying pretty high rent, I'm certainly not looking to increase that along with my Model S purchase!

Does anyone have experience with owning a Model S without a charging station at home? I really want this car, but I'm not ready to move out of the city and buy a house just yet. Thanks for any thoughts or advice!

Well, I have the same problem. But its not a short term thing, its a long term life of the pack thing. So we cant know for many years. Day to day, you will get to know how it works and when you have to charge, easy. And over time the charging stations will increase also. You are an early adopter (did you know that?) so make some calls and try to inspire some home and work entities to put in chargers.

I don't think anybody here can answer the question for you, as nobody has had the Model S long enough to know how different handling of it might change the battery longevity.

If there is to be any answer with any validity at all, it would have to come from Tesla.

My personal guess is that as long as you don't let it get too low you won't have a problem and the difference in longevity won't be measurable.

It's good to know that I'm not the only one facing "the renter's dilemma". And you're right - since we're talking about long-term battery performance, no one may know yet how much it will be impacted by sporadic charging (except maybe the Tesla engineers). I'm just trying to determine if it we're talking about a slight decline or taking years of the life of the battery.

Austin already has over 100 public charging stations in retail and park locations, but they are barely used since either A) you charge at home and don't need to top off during the day, or B) you don't charge at home but can't wait around at the mall for 5 hours to get a full charge.

To make the Model S work for renters and city-dwellers, there needs to be more charging stations in apartment buildings, but it's a bit of a chicken & the egg thing. My building said they are not planning to install chargers, because the ones at their more upscale sister building a couple blocks away are barely been used. People living in the city won't buy EV's until more apartments have chargers, and the apartments won't install chargers until more residents have EV's.

The hard truth I'm facing is that right now you realistically need a house and garage to own the Model S. If I knew that charging once every few days wouldn't cause my battery to go rapidly downhill, I would probably still take the plunge.

Hi lrotondo:

Tesla Premature Battery Degradation happens with the following 2 major factors:

1) Max Range charging.

2) complete battery depletion or bricking (can't even put the car to neutral, can't even roll the car)

Plugging every night or as much as possible allows the software to optimize the level of charging and prevent bricking as reported by 1 Roadster that was unplugged for months.

Infrequent charging is not a factor as long as you don't commit those two factors above.

You should enjoy your apartment and the Model S together with the help of infrequent charging ability from outside.

I recommend that you call ownership experience and ask this qustion.
877 798 3752

You can also charge at work -- many businesses have chargers available or could be convinced to. But yes, if you can't charge either at work or at home where your car will be parked for 8+ hours, then it is going to be harder.

You might also be able to convince your apartment to let you pay for the charger, or even just a 14-50 outlet.

Until a software update is confirmed you might want to also consider you will lose about 8 miles a day when not plugged in. Just keep that in mind too.
I was considering not always plugging mine when I first get it just to test out the parked losses. I haven't seen anything about the battery degrading from not being plugged in, just the risk for serious damage if left at zero charge.
As I said in another post. My car has been in the back of a truck for about 7 days now and Tesla is not worried about damage to the battery so why should I. I am curious what the charge will be Tomorrow when she is unwrapped.

Thanks for all the replies. It's great to have a highly supportive community around this car.

I will call Tesla to get their input as suggested and will post here if I learn anything interesting.

@Irotondo, I am in a similar situation in the bay area - renting and don't plan to buy a house for sometime. The Menlo Park store consultant convinced me that I was okay not charging for a few days a week or only on weekends. While it is optimized for nightly charging, it doesn't mean the battery will degrade if you don't charge it each night. Yes as buyers of this car, we are early adopters and have signed up to "test and report" what the actual behavior is. Having said that, I am not simply taking chances with such an expensive car, I'm pushing our apartment to install charging spots in the basement garage and I plan to charge at work or at the nearest public charger frequently - basically be prudent to keep the car healthy. Car arrives soon (Feb/Mar delivery). Can't wait!!

Beside mentioned 1) Depletion and 2) Max Range above, there are other helpful hints about Lithium-based batteries:

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_...

1) Battery Overheat: cold preserves life but with performance reduction, heat above 86°F is no no. I think Tesla battery has its own heating/cooling system so this is not a problem.

2) Discharge Cycle: The definition is different from various companies. Some want to plug in as much as possible so that MULTIPLE TIMES of charging are not counted as 1 Discharge Cycle because you didn't discharge the battery to more than a defined depth of discharge say 80%.

That number is important to marketing because Lithium battery's life is about 300 to 500 cycles. You don't want to count more cycles than you have to even though you may plug in and recharging thousands of times like crazy! Each time you count 1 more cycle is each time the battery is closer to its death!

So for worst case scenario, I discharge my battery down to more than 80% for each of 300 miles and that would be counted as 1 cycle each. I do 300 cycles which means 90,000 miles and the battery dies. That's pretty good if it happens within 8 years under the warranty and it will be replaced.

If you plan to keep the car more than 8 years, then you have to make a decision to prepay $12,000 for the 85 kWh battery or hope for the price to come down 8 years from now.

Thus, when taking in the account of 1) Depletion avoidance, 2) Max Range avoidance, 3) Overheat avoidance, and the sticky point mentioned on the thread's topic 4) Discharge Cycles counted as 300 instead of fewer, I think Model S is still compatible with renters and those who don't have an outlet to plug in at home.

@Irotondo;
Yes, there is no indication whatever that (e.g.) weekly charging without allowing very low charge levels would cause the battery to go "rapidly downhill". Frequent Max Range charging might also have a significant effect, but it sounds like your routine is well within the system's capabilities.

No worries, mate. (IMO)

I, too, am in a similar situation - no charger in my apartment's garage and none at my work. There are a couple within a mile of where we live and we plan on using them once a week. I think we should wait and watch on how it unfolds. The one reassuring thing is the battery warranty.

@Tam, thanks for the post. I had two thoughts, one saying that keeping a battery constantly charged to 100% in is not a good idea and the other saying that frequent complete discharge isn't good either. I wasn't sure how these two worked together. Now, after reading the webpage, I have a better idea. Also, how did you get 300 miles for 80% discharge? Unless you are plugging in multiple times and every 300 miles, you let the charge drop to 20%.

~ Prash.

if you plug in every night do you end up w/Max Range Charge?

@Laryrob - only if you tell it to do a max-range charge, which is not the default.

thx

Hi Prash:

Tesla advises to plug in as soon as you can, as frequently as you can. The software does not allow 100% Max Range charge by default. You have to MANUALLY slide from "standard" to "Max Range" charge to degrade the battery prematurely in exchange for 100% charge and longer range.

I use frequently advertised 300 miles for ease of calculation. You can use more precise number but the concept of daily charging vs infrequent charging is still there.

If a definition of a cycle is more than 80%, I have to run 241 miles or more in order to subtract 1 cycle from the battery's potential life of 300 cycles.

241 miles x 300 cycles = 72,300 miles then battery death.

That isn't bad either: 9,037.5 miles per year for 8 years.

Again, if it dies within 8 years, your 85kWh battery is under warranty with unlimited miles.

Could be wrong but I think the Panasonic cells used in the Model S are rated for 1000 cycle.

With regards to infrequent charging, bear in mind heat and state of charge are important. Infrequent charging in San Francisco is different from Austin. Summers are very hot in Austin and even if Tesla says they will keep the battery conditioned when not plugged in, that is only to the point of running the battery low and is still using up cycle life. Of course, if you are only averaging 20 miles per day or less then cycle life is less of a concern than calendar life. The ideal for an apartment dweller without charging access at home is to have charging access at work. This only needs to be 120V access unless you drive more than 35 miles per day. Don't do max range charges often and try not to let charge go below 20% very often either and you should be fine.

Hmmm at 30000 mikes a year, I wonder wh I'm going to do in 3 years?

Thanks Tam, thanks Koz!

And "battery death" is wrong. By industry convention, a battery is considered to have reached "end of service life" at 70% capacity. But of course there's still the 70% there! And the 8 yrs ↓ 70% is considered to have a 50:50 fudge factor, so that it's really anticipated to be around 100-(100-70)/2 = 85%. 85% x 265 = 225 ideal. Hardly "dead"!

Put another way, the real service life (down to 70%) is likely to be 16 years, not 8.

Thanks Brian for the clarification.

I just used the worst but unrealistic illustration on multiple discharge cycles if an infrequent charger has to deal with.

While a no name Lithium may last only 300-500 cycles but Koz points out that Panasonic 3.1 Ah NCR-18650A in Tesla is rated way beyond that for 1,000 cycles.

According to Panasonic's specs...

http://www.panasonic.com/industrial/includes/pdf/Panasonic-Battery-Energ...

their lithium ion batteries (including NCR18650) are rated at "over 500 cycles".

Regarding the definition of a charge cycle and charging, Apple explains it well here.

http://www.apple.com/batteries/

(I'm making the assumption that their lithium ion polymer batteries behave the same way as Panasonic's lithium ion phosphate batteries.)

That said, the more you replenish the charge of the battery pack, the faster you'll go through your batteries lifetime charge cycles. Let's say you have two cars each with an 85 kWh battery (or 60 or 40). Car A you charge one only once a week and Car B you charge whenever it's not being driven (i.e. at work and at home). Let's also assume you only drive both cars the same distance to work (and nowhere else) each day under the same conditions.

Charging Car B will replenish the energy used for the only for the miles driven, but Car A will replenish the energy for the miles driven plus the vampire load of the car (2.4 kWh per day or about 8 miles of range assuming 300 Wh/mile). At the end of the week, Car A will have gone through more of the batteries charge cycles than Car B because of the vampire load. If we extrapolate this scenario out several years, we can see how the range of Car A will be less than that of Car B even though both cars were driven the same number of miles under the same conditions. I believe this is why Tesla recommends plugging in the car whenever possible.

@paul_villasenor - In your example, would you say that Car B will have a lower electric bill than Car A or about the same?

If the car handles the "powered off" loads the same (same energy use), then Car B would have a lower bill due to avoiding battery charge/discharge losses for these loads.

If an apartment has a 110v outlet near the car, an overnight charge will easily maintain a 20 mi/day RT commute. So many people don't bother with 110v, but for short commutes it is so much easier on the battery than the once/wk charge. That also keeps the vampire load off the battery for 1/3 of it's life.

Tesla recommends charging nightly or basically whenever you can. the owner guide specifically states LEAVE YOUR MODEL S PLUGGED IN!

I might add that a charge cycle is considered a full discharge/charge cycle.

@superliner-

Yes, the manual states to leave the car plugged in, but after extensive discussions on this specific topic with multiple ownership experience representatives and my delivery specialist, it's clear that Tesla in NOT requiring this as a condition for maximal battery longevity, and that it is a general recommendation for the general public who might be prone to allow the battery to reach a highly discharged state. As mentioned above, there is no present concern that intermittent charging should have a detrimental effect unless the battery is repeatedly depleted to whatever % depth constitutes a full discharge cycle.

I only skimmed through the posts, so I apologize if I am repeating.

I think the more important question about off-site occasional charging is: are your sure you want an EV in that situation? - seems like the worst of both worlds in terms of convenience. The beauty of home charging a model S is always having a full charge each morning. Off site charging every few days is like having an ICE, except it takes hours to fill the tank. As a temporary situation or if charging at work is possible, it might be okay, but otherwise I would be hesitant.

Just my opinion and if it works for you, fantastic! Great car from what I hear!


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