Advice Please: Charge Every Night or Not

[MSEV]

I have a short commute to work (6.5 mi). I may have another short errand to do on the way home, taking me up to 20 mi round trip. I believe Tesla recommends that you plug in every night. I wonder about things like the number of cycles of the battery.

I have been charging to 80%, but only on the weekends. During the week I don't plug in unless any type of trip or demand on energy would be coming up the next day. Is this ok? Might this extend the battery life or should I plug in every night for the longest battery life?

 

[gg_got_a_tesla]

Short answer: don't worry about it. Plug in as often as it's convenient for you.

Slightly long answer: "they" say that several shallow cycles are better than fewer deep cycles for long term health of Li ion batteries in general. So, plugging in even when you consumed only 20 miles of range is purportedly better than waiting for a few days to plug in for longer.

 

[tiblot]

In general all li-ion batteries like to charge cycle somewhere in the 40-70% range for best case scenario. In real world settings, if you're worried, set the daily charge limit to 70%. Otherwise, no reason to worry about it at all.

I have a 4 mile commute and I end up charging once every 3-4 days or when ever i feel like it. But it doesnt matter if you charge to the 90% daily max ever single day. Just plug in when convenient and no worries!

 

[rickgt]

I typically only put on 50-70 miles a week, between trips of longer distance. I usually charge once or twice a week to the 80% level

 

[tiblot]

Honestly, the only two rules you really need to follow:

1. Don't goto 0%.
2. Don't goto 100% and leave it overnight.

 

[TexasEV]

When I got my car two years ago it came with a card inside that said "A connected Model S is a happy Model S". You should plug it in every night if you have the opportunity, and let the battery management system manage the battery. Follow the owners manual and keep it plugged in when possible:

"The most important way to preserve the Battery is to LEAVE YOUR MODEL S PLUGGED IN when you are not using it."

and

"There is no advantage to waiting until the Battery’s level is low before charging. In fact, the Battery performs best when charged regularly."

I don't think the instructions could be any clearer.

 

[scottm]

I leave my car plugged in all day at work sucking whatever juice it can from 120/16A circuit, never fills up past 90% and each day I get home with nearly how much I left in the morning with. Just short by a couple percent.

Drive all week doing just that, not plugging in at home. Each morning I might be down 1 more percent due to passive draining (vampire load).

By Friday the level has usually gotten to 50% or lower when I get home after work, and I plug in HPWC to 90% and get ready for Saturday a.m. to do as I please on weekends. I home charge as needed on the weekend to be at 80% to start off Monday morning for work.

 

[efusco]

When I got my car two years ago it came with a card inside that said "A connected Model S is a happy Model S". You should plug it in every night if you have the opportunity, and let the battery management system manage the battery. Follow the owners manual and keep it plugged in when possible:

"The most important way to preserve the Battery is to LEAVE YOUR MODEL S PLUGGED IN when you are not using it."

and

"There is no advantage to waiting until the Battery’s level is low before charging. In fact, the Battery performs best when charged regularly."

I don't think the instructions could be any clearer.

This exactly. Will you destroy and cause irreparable harm to your battery by plugging in only on the weekend? Probably not much, and probably nothing that would show for years. But this car has a very complex battery management system, it comes on frequently to check the condition and optimize the condition. It's a ~$45,000 battery. Why NOT plug it in daily (if it isn't terribly inconvenient to do so). It's a good habit to get into, it's what Tesla says you should do, and it keeps you topped up in case you need to break from your routine and go on a longer trip, unexpectedly, and need the extra range.

 

[ReddyLeaf]

Don't worry about it. With such low driving needs, the battery will degrade more from time than from cycle use. If you want to maximize the amount of battery use, then drive 100,000 mi per year. In ten years, after 1 million miles, you might be down to 60-70%. However, after ten years the battery will probably still degrade 10% even if only lightly used (say 100,000 mi). The point is use the car NOW as much as possible BEFORE the battery degrades. In ten years and unused battery and a used battery will both still be degraded. I drove all of my long range trips LEAF trips in the first 3-4 years. Now I'm down 20% (50-80 mi range) and out-of-town trips are much more difficult.

 

[spottyq]

Don't worry about it. With such low driving needs, the battery will degrade more from time than from cycle use. If you want to maximize the amount of battery use, then drive 100,000 mi per year. In ten years, after 1 million miles, you might be down to 60-70%. However, after ten years the battery will probably still degrade 10% even if only lightly used (say 100,000 mi). The point is use the car NOW as much as possible BEFORE the battery degrades. In ten years and unused battery and a used battery will both still be degraded. I drove all of my long range trips LEAF trips in the first 3-4 years. Now I'm down 20% (50-80 mi range) and out-of-town trips are much more difficult.

It would really be useful to get information on battery degradation versus time for Tesla's batteries. (They is some info for degradation versus miles driven, and it is quite good actually.)

 

[Barry]

Set your charge to 60% instead of 80% for work days and plug it in every night.

 

[MSEV]

Set your charge to 60% instead of 80% for work days and plug it in every night.

Barry,
Why?

 

[dadaleus]

Barry,
Why?

Because you don't want to charge any higher than you need to. I try to keep my battery above 50%, but not charge it to a higher level than needed to keep it above 50%.

 

[andydoty]

I charge every night to the default setting of 90%. My reasoning is that our lives are unpredictable and you never know if you're going to have to take an impromptu drive. I've taken long trips and actually briefly stopped at the local supercharger to insure I have around 200 miles or so in the "tank". Especially in the winter as the heat uses a great deal of power. You may be able to skimp slightly in spring or fall, however, the summer and winter draw a great deal of power. Just my thoughts...

 

[ReddyLeaf]

It would really be useful to get information on battery degradation versus time for Tesla's batteries. (They is some info for degradation versus miles driven, and it is quite good actually.)

Yes, but there can also be a bias in the data. High mileage cars in short periods of time (less than 3 years) cannot be easily compared to low mileage cars in long periods (more than 10 years). Also, there are no 10 year old Model S batteries yet. There is good data on the Roadster battery, and yes, mileage seems to be the most important variable. Lithium ion batteries are thought to be good for about 1000 to 2000 cycles if treated properly (moderate temperature, slower charge/discharge). If the Model S travels about 250 to 300 miles on a single charge, then 1000 cycles will be 250,000 to 300,000 miles. For 2000 cycles (which the S should easily handle before seeing 20% degradation), you would need to drive over 500,000 miles. It's no wonder that Tesla provides an unlimited mile battery warranty on the 85 kWh battery. We will have to wait until 2020 or 2025 to find out if degradation follows this expected curve.:wink: Unfortunately, there are already numerous reports of battery replacements under warranty for other issues (engineering related, not range degradation).

 

[Candleflame]

Batteryuniversity has some detailed info (unfortunatley not for low SOC...) regarding degradation.

I'm just gonna assume Tesla's cooling&heating will keep the pack somewhere around 25°C or colder when the car isn't in use. As we can see charging to 100% for a road trip really isn't that bad, even if you leave the car at 100% over night. You degrade about 5x faster, which for a few hours doesn't really matter. If it's cold outside it's even less relevant. And almost certainly doesn't matter if you charge 100% at a SC and drive off immediatley. So from that point of view I really would just keep the car plugged in and set the SOC to 80% or if going on a roadtrip 100% the night before.

Then theres also how frequently you do discharges.

So for once you can't completly discharge a Model S, I think only 73kw are "driveable"?. As such we can assume that we probably get 500 solid cycles out of the battery before battery degradation really kicks in. With quick driving (130kmh) that would give you about 150000km on the odometer. If you only charge to 80% and drive it all off that will give you about twice as much. Are you sure you will still be driving your current battery or car after 300k kilometers? I think more frequent charging cycles will also further increase battery life but I am not sure how much. (So Charging every day from 50% to 80% is better than 10 - 80% every 3r day). So i'd probably plug it in as much as possible.

In reality those numbers will be much better due to Teslas battery management and the fact that you can't fully discharge the battery anyways. Certainly Bjorn has only noticed much degradation after 90k kilometers.

 

[MSEV]

Thanks to everyone. It's nice to have a better understanding of what is going on in dealing with such an important battery.

 

[MyJoule]

I will chime in- my motto " A happy Tesla is a plugged in Tesla" that way it can keep SOC at whatever you set it for and it's ready to go when you are. I charge to 90% unless heading on a long trip- then of course I top off to 100% just before I leave. 10K miles 0 degradation ..

 

[dsm363]

I will chime in- my motto " A happy Tesla is a plugged in Tesla" that way it can keep SOC at whatever you set it for and it's ready to go when you are. I charge to 90% unless heading on a long trip- then of course I top off to 100% just before I leave. 10K miles 0 degradation ..

I agree. There is just too much that goes on in life to worry about this. Set it to 80 or 90% and don't word about it.

Of course if you never drive more than 10 miles in a day or so and want to drop that more nothing wrong with that either.

 

[Larry Chanin]

Batteryuniversity has some detailed info...

Also from Battery University:

How to Prolong Lithium-based Batteries

Similar to a mechanical device that wears out faster with heavy use, so also does the depth of discharge (DoD) determine the cycle count. The shorter the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses. Partial discharge on Li-ion is fine. There is no memory and the battery does not need periodic full discharge cycles to prolong life. The exception may be a periodic calibration of the fuel gauge on a smart battery or intelligent device. (See BU-701a: How to Calibrate Batteries)

Larry