I've read posts by some owners who contend that an occasional Range charge enables better cell balancing and is a good trade off in the sense that a battery pack that's not balanced will have lower performance and unevenly stress the individual cells. Whether or not that's actually the case, it makes a good story. Has Tesla published anything in support of this?
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I've read posts by some owners who contend that an occasional Range charge enables better cell balancing and is a good trade off in the sense that a battery pack that's not balanced will have lower performance and unevenly stress the individual cells. Whether or not that's actually the case, it makes a good story. Has Tesla published anything in support of this?
gg_got_a_tesla
Model S: VIN 65513, Model 3: VIN 1913
Excellent thread, dave! Been meaning to pose some of these questions myself.
I'm going the route of topping off in Standard mode every night and am also practically topping off via a 110V outlet at work (given my 27-mile one way commute and being at work for 8-9 hours). Shallow cycles is what I'm going for but, staying under 90% SoC.
I have been concerned about this. At night, I can reclaim the 27 miles from my 14-50 in an hour but, can throttle down to 5A and charge overnight instead. Would like to know which one'd be better, even if it's only marginally.
The other factor in the fast vs slow charging decision is the efficiency of the charging process. According to tomsax's blog, charging at lower amperages is less efficient and hence consumes more electricity than charging at higher amperages:
Tesla Roadster Charging Rates and Efficiency - Tom Saxton's Blog
I'm going the route of topping off in Standard mode every night and am also practically topping off via a 110V outlet at work (given my 27-mile one way commute and being at work for 8-9 hours). Shallow cycles is what I'm going for but, staying under 90% SoC.
I have been concerned about this. At night, I can reclaim the 27 miles from my 14-50 in an hour but, can throttle down to 5A and charge overnight instead. Would like to know which one'd be better, even if it's only marginally.
The other factor in the fast vs slow charging decision is the efficiency of the charging process. According to tomsax's blog, charging at lower amperages is less efficient and hence consumes more electricity than charging at higher amperages:
Tesla Roadster Charging Rates and Efficiency - Tom Saxton's Blog
The question has two parts. First the behaviour of lithium batteries must be understood. Only then can we move on to what Tesla does.
First, the less that battery pack is discharged before recharge, then the longer it will last. 5 discharges at 20% means the battery pack hardly degrades. A 100% discharge means it is lost one complete discharge cycle in its life expectancy. Better battery solutions will not let you discharge past 50% since most battery degrading occurs at that second 50% discharge.
Second, charging too often can also be problematic. Discovering the charge state of a battery means significant charging (possible overcharging) is required to learn a battery's state. Therefore if a charger remains connected, then it fully charges a battery once. And need not try to recharge (overcharge) a battery again to learn a battery's charge state.
Third, what is the full charge voltage of a lithium battery? That voltage changes with temperature and other parameters. Those parameters also change what the charger sees to determine battery states.
Four, lithium batteries work without harm is cold weather. Storage is cold weather prolongs battery life expectancy. However recharging a cold lithium battery causes faster degradation. One typical numbers suggests lithiums must be above 40 degrees F (5 degrees C) to recharge.
Now, these above characteristics are known to Tesla. What does Tesla's computer algoritym do? We know the car computer will not let the battery recharge when too cold. But what is considered too cold? Will it charge at lower temperatures because it thinks you need the car soon?
Its computer can monitor battery useage. And usually predict whether to charge a battery to determine its charge state. However, constant unplugging and reconnecting could add wild card changes. Encouraging the computer to 'top off' a fully charged battery more often.
One factor a computer cannot compensate for is excessive discharges between recharges. Plenty of smaller discharges rather than single full discharge means battery life expectancy will be significantly longer.
Again, the question requires two answers. First is charactertistics of lithium (and those change with different lithium designs). Second, what Tesla's computer does.
+1. This is a very interesting read. I have a 20 mile commute total each day and am very interested to hear what people recommend for charging. My work has 110 stations and a Blink charger, but I assume I don't need to use the latter with any regularity.
Great questions. I wish I had iron clad answers, but I’ll share what I’ve concluded. I’ve been trying to find quantifiable answers to this kind of stuff for a couple years with the Leaf. It has lead me to read up quite a bit on Li-ion batteries. Battery University has some great articles on this. Unfortunately, when it comes to the S, it’s hard to do anything but speculate beyond what Tesla has put forth officially. Here is my personal and unofficial -work in progress- perspective, I do not claim to be an authority on this.
-WHY do I need to keep the car plugged in all the time?
There are likely several reasons for why Tesla recommends this.
1. First and foremost, I believe Tesla wants owners to have a very simple protocol to follow that makes owning the car as stress free as possible. The simplest thing to do to avoid disappointing experiences is to have the car charged up whenever convenient. Charging up all the time will also likely reduce the number of times someone complains of having too much tedium to deal with in regards to managing the EV ownership experience.
2. Secondly, keeping the car plugged in protects the battery from at least a couple of scenarios. With the car plugged in, the car can easily manage the batteries temperature, protecting it from extreme heat and cold which can be permanently damaging. Tesla got some bad press from some Roadster owners who left their cars unplugged for prolonged periods and caused the batteries to “brick”, a term used to describe a battery that has lost so much voltage that it can’t “wake up” again. Bricking these batteries requires a complete pack replacement, and is something expressly not covered under the warranty.
3. Having the car plugged in makes it easy to precondition the battery before driving, bringing it to the ideal operating temperature and thus have a more ideal range without draining the battery.
4. Having the car plugged in keeps the “vampire loads” from taking a bite out of the cars range, since they draw from shore power instead.
If you are willing to take on the responsibility to “manage” the battery yourself, assuring the car avoids damaging extreme temperatures, assuring the charge doesn’t fall critically low, plugging it in to precondition the battery before heading out if you need maximum range in cold weather and generally managing the state of charge yourself, thinking ahead enough to not fall short, I don’t see why it would be bad for the battery to be left unplugged. Granted, that’s a whole lot more than most people want to think about. I am the kind of person who is willing to do some of that managing at least some of the time and take on the added risk, as I live in a moderate climate and am comfortable with my understanding of what makes these things tick.
Are there battery health benefits to keeping it as fully charged as possible, or is this just to prevent people from "Brodering" it and accidentally draining the battery?
From the urban dictionary, “Brodering” would suggest the effect was intended :~). My hunch is that keeping the battery charged up is primarily to improve the customer experience. It’s ideal for Li-ion batteries to stay at a resting state of about 50% and be charged up close to the time of use, enough to have them back to around 50% when done performing their task. That of course is not practical for a lot of folks. The standard mode is designed to take most of the thinking out of the process but undoubtedly leads to faster decline than a more micro management approach, if done correctly. How much of a difference will it make to manage all this yourself? It’s hard to say and there is undoubtedly some risk to making up your own protocol, all my efforts may prove innocuous or worse. I can say this with certainty, the li-ion batteries I have owned that I paid no attention to with respect to charging habits tended to have a short life, the one’s I have paid a lot of attention to mostly by storing them half charged tend to last a very long time. That said, none of my devices other than the Leaf, have had a “standard” mode and even the Leaf doesn’t have anything nearly as sophisticated as the Tesla S’s BMS. What makes the S different to me, is that unlike devices that have user replacable batteries that need only last a few years, I want the S's batteries to last one to two decades, so I'm more motivated to take really good care of them!
Does the battery management system behave differently if plugged in, vs. not plugged in?
Yes, at least if the battery is charged just prior to use or the battery is conditioned just prior to use, in either case it will be warmer and provide a more optimal range, compared to being cold, when this is done while plugged in the battery conditioner won't eat up range. If the ambient temps are extreme, again, the BMS protects the battery. If it’s left unplugged, it’s ability to protect the battery is limited. Extremely hot or cold climates require extra caution.
Is battery longevity affected by the state of charge while not in use? If so, do I understand that 90% is better than 100% when sitting in my garage? If 90% is better than 100%, is 80% even better than 90%? What about 5% or less, is that harmful?
The worst scenario is leaving the battery at a “max range” charge level for prolonged periods. It’s shades of gray below the 85% (some are saying 90%) state of charge.
What actually causes battery degradation? Is it the charging or the discharging? Does the SPEED of charging or discharging affect it?
My understanding is that high states, above true 80% SOC, cause dramatically accelerated rates of cladding of the anode and cathode of any Li-ion battery, leading to premature age related capacity decline. Since we don’t really know exactly how “big” the 85 kW S battery is, a standard charge may be within the true 80% limit… maybe someone has these calculations, I don’t. High temperature is one of the main Li-ion battery killers, typically high ambient temps have more of a cumulative effect because the exposure is constant whereas high heat from repetitive fast charging/discharging is short in duration and the S has temperature management and is designed to substantially mitigate the effect of rapid charging/discharging heat spikes. Temperature management requires more energy in extreme climates, hence the recommendation to keeping the car plugged in to prevent it from becoming too depleted for the BMS to perform it’s task.
Is there an optimum charging amperage for battery health if the time involved was not a concern? I've heard that Superchargers are bad for battery life, but then I've also heard the opposite. Does anyone know for sure? Does the battery degrade based on time, or usage? Both?
I can’t offer certainty and actual mileage may very :~). That said, rapid charging doesn’t really seem to effect Li-ion’s much per say, at least from what I can tell from owning and reading up on the Leaf, it’s more a matter of keeping the battery cool, and again, with temperature management, the S should be able to handle continuous high speed driving and fast charging much better than the Leaf. With the Leaf, continuous high speed driving and fast charging beyond a few cycles can lead to a very hot battery. The only reason I can see to slow down the rate of charge in a car like the S that has active cooling is to time it more ideally for overnight charging in cold climates where you want the charge to end close to the time you need to use the car, as a way of keeping the battery warm or “conditioned”. Then again, it appears that using the prewarming function “conditions” the battery pretty quickly, so it’s pretty easy to condition the battery before one leaves in the morning if it’s very cold, even if the charging was rapid and ended many hours before the departure time.
Does the length of a charge matter? Is it better for the battery to have one giant charge from 10% to 90%, or multiple tiny charges keeping it "topped off"?
There seems to be at least some consensus that shallow cycling, avoiding extremes, either above 85% or below say 30% SOC is best for long term life. I’ve read studies that, for instance, put the typical li-ion cell cycle life around three thousand if charged full from empty each time, whereas shallow mid SOC charging can extend cumulative cycle life into the tens of thousands. Plug in hybrids like the Volt employ a shallow mid pack charging approach, I’m told it’s the inner 30% of the packs capacity, intended to dramatically extend the battery life by being very easy on the battery pack. Avoiding the low end of the battery is thought to be good because in the lower end there is greater resistance and more potential for stress on the battery.
Does ambient temperature matter, considering that the battery has it's own internal temperature control mechanisms? Is it worse for the battery if I leave my car parked outside in the winter, or should I bring it in the garage?
From everything I’ve read, it appears that keeping the battery cool, almost the cooler the better, within reason, is ideal for life, but not ideal for output. Many hobbyists who use Li-ion cells for things like remote controlled airplanes or helicopters have devised some rather interesting protocols for extending battery life, typically keeping them stored at 50% SOC and in the fridge. The downside with leaving the S outside over night in the cold would be that the BMS would only keep the battery warm while charging, unless it’s truly extreme cold. Once finished charging, the temp drops and would require conditioning in the morning on shore power to achieve maximum range.
I’ll say it one final time, these are my observations, speculations and in some cases guestimations, it’s very much a work in progress.
I don’t know how fastidious about this I will be with the S, I’m still feeling it out. With the Leaf it became second nature. If I needed a max charge I wouldn’t hesitate to charge to 100% right before I needed it but the vast majority of time I only drive 30-40 miles a day so I would charge the car up to around 50%, leave it over night, and top up in the morning before I needed to use the car. If the car ended up being between 50 and 80% when I arrived home, I would call it good, even above 40% was considered fine, but below that and I would top up before letting it sit overnight, anything above 80% and I’d drive it down or park it and run the climate control till the SOC came down. With the S, the iphone app allows for stopping and starting the charging, which is very nice, as the Leaf only allowed me to start the charge and would override the timer and charge to 100%. Being able to stop and start the charge remotely as well as change from standard to max range on the S through the app makes being gentle on the battery extra easy. Who knows though, I may get leery of diverging from the official Tesla protocol or just plain lazy and start plugging it in whenever, time will tell.
-WHY do I need to keep the car plugged in all the time?
There are likely several reasons for why Tesla recommends this.
1. First and foremost, I believe Tesla wants owners to have a very simple protocol to follow that makes owning the car as stress free as possible. The simplest thing to do to avoid disappointing experiences is to have the car charged up whenever convenient. Charging up all the time will also likely reduce the number of times someone complains of having too much tedium to deal with in regards to managing the EV ownership experience.
2. Secondly, keeping the car plugged in protects the battery from at least a couple of scenarios. With the car plugged in, the car can easily manage the batteries temperature, protecting it from extreme heat and cold which can be permanently damaging. Tesla got some bad press from some Roadster owners who left their cars unplugged for prolonged periods and caused the batteries to “brick”, a term used to describe a battery that has lost so much voltage that it can’t “wake up” again. Bricking these batteries requires a complete pack replacement, and is something expressly not covered under the warranty.
3. Having the car plugged in makes it easy to precondition the battery before driving, bringing it to the ideal operating temperature and thus have a more ideal range without draining the battery.
4. Having the car plugged in keeps the “vampire loads” from taking a bite out of the cars range, since they draw from shore power instead.
If you are willing to take on the responsibility to “manage” the battery yourself, assuring the car avoids damaging extreme temperatures, assuring the charge doesn’t fall critically low, plugging it in to precondition the battery before heading out if you need maximum range in cold weather and generally managing the state of charge yourself, thinking ahead enough to not fall short, I don’t see why it would be bad for the battery to be left unplugged. Granted, that’s a whole lot more than most people want to think about. I am the kind of person who is willing to do some of that managing at least some of the time and take on the added risk, as I live in a moderate climate and am comfortable with my understanding of what makes these things tick.
Are there battery health benefits to keeping it as fully charged as possible, or is this just to prevent people from "Brodering" it and accidentally draining the battery?
From the urban dictionary, “Brodering” would suggest the effect was intended :~). My hunch is that keeping the battery charged up is primarily to improve the customer experience. It’s ideal for Li-ion batteries to stay at a resting state of about 50% and be charged up close to the time of use, enough to have them back to around 50% when done performing their task. That of course is not practical for a lot of folks. The standard mode is designed to take most of the thinking out of the process but undoubtedly leads to faster decline than a more micro management approach, if done correctly. How much of a difference will it make to manage all this yourself? It’s hard to say and there is undoubtedly some risk to making up your own protocol, all my efforts may prove innocuous or worse. I can say this with certainty, the li-ion batteries I have owned that I paid no attention to with respect to charging habits tended to have a short life, the one’s I have paid a lot of attention to mostly by storing them half charged tend to last a very long time. That said, none of my devices other than the Leaf, have had a “standard” mode and even the Leaf doesn’t have anything nearly as sophisticated as the Tesla S’s BMS. What makes the S different to me, is that unlike devices that have user replacable batteries that need only last a few years, I want the S's batteries to last one to two decades, so I'm more motivated to take really good care of them!
Does the battery management system behave differently if plugged in, vs. not plugged in?
Yes, at least if the battery is charged just prior to use or the battery is conditioned just prior to use, in either case it will be warmer and provide a more optimal range, compared to being cold, when this is done while plugged in the battery conditioner won't eat up range. If the ambient temps are extreme, again, the BMS protects the battery. If it’s left unplugged, it’s ability to protect the battery is limited. Extremely hot or cold climates require extra caution.
Is battery longevity affected by the state of charge while not in use? If so, do I understand that 90% is better than 100% when sitting in my garage? If 90% is better than 100%, is 80% even better than 90%? What about 5% or less, is that harmful?
The worst scenario is leaving the battery at a “max range” charge level for prolonged periods. It’s shades of gray below the 85% (some are saying 90%) state of charge.
What actually causes battery degradation? Is it the charging or the discharging? Does the SPEED of charging or discharging affect it?
My understanding is that high states, above true 80% SOC, cause dramatically accelerated rates of cladding of the anode and cathode of any Li-ion battery, leading to premature age related capacity decline. Since we don’t really know exactly how “big” the 85 kW S battery is, a standard charge may be within the true 80% limit… maybe someone has these calculations, I don’t. High temperature is one of the main Li-ion battery killers, typically high ambient temps have more of a cumulative effect because the exposure is constant whereas high heat from repetitive fast charging/discharging is short in duration and the S has temperature management and is designed to substantially mitigate the effect of rapid charging/discharging heat spikes. Temperature management requires more energy in extreme climates, hence the recommendation to keeping the car plugged in to prevent it from becoming too depleted for the BMS to perform it’s task.
Is there an optimum charging amperage for battery health if the time involved was not a concern? I've heard that Superchargers are bad for battery life, but then I've also heard the opposite. Does anyone know for sure? Does the battery degrade based on time, or usage? Both?
I can’t offer certainty and actual mileage may very :~). That said, rapid charging doesn’t really seem to effect Li-ion’s much per say, at least from what I can tell from owning and reading up on the Leaf, it’s more a matter of keeping the battery cool, and again, with temperature management, the S should be able to handle continuous high speed driving and fast charging much better than the Leaf. With the Leaf, continuous high speed driving and fast charging beyond a few cycles can lead to a very hot battery. The only reason I can see to slow down the rate of charge in a car like the S that has active cooling is to time it more ideally for overnight charging in cold climates where you want the charge to end close to the time you need to use the car, as a way of keeping the battery warm or “conditioned”. Then again, it appears that using the prewarming function “conditions” the battery pretty quickly, so it’s pretty easy to condition the battery before one leaves in the morning if it’s very cold, even if the charging was rapid and ended many hours before the departure time.
Does the length of a charge matter? Is it better for the battery to have one giant charge from 10% to 90%, or multiple tiny charges keeping it "topped off"?
There seems to be at least some consensus that shallow cycling, avoiding extremes, either above 85% or below say 30% SOC is best for long term life. I’ve read studies that, for instance, put the typical li-ion cell cycle life around three thousand if charged full from empty each time, whereas shallow mid SOC charging can extend cumulative cycle life into the tens of thousands. Plug in hybrids like the Volt employ a shallow mid pack charging approach, I’m told it’s the inner 30% of the packs capacity, intended to dramatically extend the battery life by being very easy on the battery pack. Avoiding the low end of the battery is thought to be good because in the lower end there is greater resistance and more potential for stress on the battery.
Does ambient temperature matter, considering that the battery has it's own internal temperature control mechanisms? Is it worse for the battery if I leave my car parked outside in the winter, or should I bring it in the garage?
From everything I’ve read, it appears that keeping the battery cool, almost the cooler the better, within reason, is ideal for life, but not ideal for output. Many hobbyists who use Li-ion cells for things like remote controlled airplanes or helicopters have devised some rather interesting protocols for extending battery life, typically keeping them stored at 50% SOC and in the fridge. The downside with leaving the S outside over night in the cold would be that the BMS would only keep the battery warm while charging, unless it’s truly extreme cold. Once finished charging, the temp drops and would require conditioning in the morning on shore power to achieve maximum range.
I’ll say it one final time, these are my observations, speculations and in some cases guestimations, it’s very much a work in progress.
I don’t know how fastidious about this I will be with the S, I’m still feeling it out. With the Leaf it became second nature. If I needed a max charge I wouldn’t hesitate to charge to 100% right before I needed it but the vast majority of time I only drive 30-40 miles a day so I would charge the car up to around 50%, leave it over night, and top up in the morning before I needed to use the car. If the car ended up being between 50 and 80% when I arrived home, I would call it good, even above 40% was considered fine, but below that and I would top up before letting it sit overnight, anything above 80% and I’d drive it down or park it and run the climate control till the SOC came down. With the S, the iphone app allows for stopping and starting the charging, which is very nice, as the Leaf only allowed me to start the charge and would override the timer and charge to 100%. Being able to stop and start the charge remotely as well as change from standard to max range on the S through the app makes being gentle on the battery extra easy. Who knows though, I may get leery of diverging from the official Tesla protocol or just plain lazy and start plugging it in whenever, time will tell.
Al Sherman
It's about THIS car.
Nice. What about heat? Not from usage. Just sitting in a hot garage. My garage can get pretty hot in the Summer. Does the BMS actually cool the battery when it's plugged in, in hot ambient temps?
waidy
Member
100thMonkey, thank you so much for sharing your understanding in battery management. I appreciate it. I, like you, am doing pretty much the same "micro-managing" charging: i.e. charge only when SOC < 50%. Do you know, to your knowledge, whether the S's BMS perform cell balancing when SOC != 100% ? If so, how does it determine what is the voltage level to balance ?
There's been extensive discussion on Nissan Leaf Forum - Online forum for the Nissan Leaf Electric Car, in a number of threads, on the topic of maximizing Li-ion calendar life. The consensus seems to be that lower SOCs are better for "storage", down to about 30%. Lower battery temperatures, down to maybe 0 Celsius, are quite helpful. We normally time our charging (via timer on the car) to end just before we need to use it, so that the battery spends the majority of its time at lower SOCs. I would probably try to do something similar if I owned a Tesla, except in hot weather, when I'd keep the car plugged in to make sure the battery pack is kept cool by the TMS. Using an 'S' as a daily commuter, there's really no need to charge all the way up to 90% all of the time if you want to "baby" the battery pack for maximum life.
As for driving, the voltage at 30-60% SOC is still reasonably high and not a problem at all. Note that 30-60% is the approximate SOC range used in the Mars rover (Spirit/Opportunity) Li-ion batteries for longevity. Down to maybe 10-20% SOC, voltage declines in Li-ion batteries tend to be pretty gradual. For battery longevity, I certainly wouldn't advise flooring the pedal and pulling maximum current at a low SOC (below maybe 20%).
Also, our 2011 Leaf charges at only 3.3 kW, so charging is pretty easy on the 24 kWh pack. Given the much larger battery pack on the 'S', charging at 10 kW should be similarly gentle on its pack.
As for driving, the voltage at 30-60% SOC is still reasonably high and not a problem at all. Note that 30-60% is the approximate SOC range used in the Mars rover (Spirit/Opportunity) Li-ion batteries for longevity. Down to maybe 10-20% SOC, voltage declines in Li-ion batteries tend to be pretty gradual. For battery longevity, I certainly wouldn't advise flooring the pedal and pulling maximum current at a low SOC (below maybe 20%).
Also, our 2011 Leaf charges at only 3.3 kW, so charging is pretty easy on the 24 kWh pack. Given the much larger battery pack on the 'S', charging at 10 kW should be similarly gentle on its pack.
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Merrill
Merrill
Ok, now I need some clarification on the state of the battery charge. I read that Tesla recommends keeping the car plugged in, so the first thing that is wrong about this is that in most states the cost of electricity varies. So you would not want to plug in 24/7 and the pay the higher cost during the day. Then you read that Tesla says not to keep the battery at a full state of charge, better to let the the state of charge go down a little and then charge up. I know this is somewhat simplistic but can someone clear this up.
If the S is like the Roadster, it can definitely balance the pack on just a standard charge, but like all battery packs, the difference between cell balance shows up better at high SOC.
One thing to keep in mine when "micro-managing" the SOC of the pack - in warm/hot weather it could definitely be beneficial to keep it plugged in as much as possible depending on what parameters the car uses to cool the pack. Until we figure out exactly what parameters the car uses to manage pack temperatures, it's certainly not a bad idea to leave it plugged in all the time when the weather warms up.
If I lived in an area that got hot in the summer I would keep the car plugged in! From reading here about mitigating cold weather effects you can keep the car plugged in and charging at a slow pace to keep the SOC down while still engaging the battery conditioning system, it would stand to reason that the same technique would be valuable in hot climates. Nissan Leafs below the 33/34rd parallel or thereabouts have had an especially tough time, experiencing relatively rapid and permanent degredation over a short period of time, for lack of a monitoring and cooling system for the batteries. Leaving the car out in the sun on a very hot day can presumably do even more damage. you can google "baking cookies on your dashboard in Phoenix Arizona" to get a better sense of just how bad things can get. The inside of a car in direct sunlight can get upwards of 185F in a place like Phoenix, essentially becoming an oven and even though heat rises and the batteries are low, I speculate that the mass of the car becomes heated as well creating radiant heat that can penetrate downward. It's conceivable, though we don't have hard numbers, that this could accelerate aging of batteries or even worse, lead to sudden decline. I'm not saying this to create fear, more as a special caution from leaving the car unplugged in hot weather. Thankfully Tesla has provided a very smart and capable battery conditioning system. they are, IMHO, a few steps ahead of their competition, no actually I'll say it differently, I don't think Tesla really has any competition being so far ahead of the pack on so many levels.
If you are at all inclined to worry about screwing up, follow the rules and plug in and just enjoy the car... be good, or be good at it!
+1, what he said!
I have no idea if cell balancing can be performed at anything but a full charge but I wouldn't put it past Tesla to create a BMS smart enough to do it at at least the standard charge if not continuously. Out of an abundance of caution, it seems prudent if you are keeping the car at 50% SOC most of the time to occasionally, maybe once a month, run it down to 30% and charge it up all the way to "max range", time it so it completes the charge several hours before you drive. I don't know how the S differs from the Leaf in this way, but the Leaf takes a few hours to complete the process while plugged in... can't imagine that would hurt. In my mind it's mostly a numbers game where I am simply eliminating the bulk of times the car sits at a high SOC.
If someone discovers that the S is holy unique to all other battery operated devices with respect to battery aging and SOC I will gladly retract all of this, but for now I'm going with the idea that it is probably worth a bit of micro managing. with the S, the battery is so huge, that for most day to day driving, keeping it at a lower SOC really is not an inconvenience, at least not so far.
Al Sherman
It's about THIS car.
"If I lived in an area that got hot in the summer I would keep the car plugged in!"
So, does the BMS actually keep the pack at a lower than ambient temperature on a really hot Summer day when the car is plugged in?
So, does the BMS actually keep the pack at a lower than ambient temperature on a really hot Summer day when the car is plugged in?
Daniel Scherer
Junior Member
Heat is the enemy of batteries and chargers so if you aren't in a hurry then drop the charge rate down to match the time you have to get the job done. I am an electric lift truck mechanic and have years of experience with DC and AC drives as well as lead acid batteries and chargers. Cold saps battery power but heat destroys them.
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The cells should balance themselves as if one has a higher state of charge that will flow over to ones that don't. Equalize charging in lead acid batteries is a slow steady long charge.
- - - Updated - - -
The cells should balance themselves as if one has a higher state of charge that will flow over to ones that don't. Equalize charging in lead acid batteries is a slow steady long charge.
The question is, what temperature range does it aim for and under what conditions?
For example, the Volt has different temperature targets for it's pack which depend on operation state (plugged in or not, on or not) and SOC (once SOC drops below a certain point and the car is not plugged in or on, the TMS system has a higher temperature threshold). There's no reason to believe that Tesla wouldn't do the same.
Obviously the goal is to meet some minimum durability target and to use the least amount of energy while doing so (among others).
I suspect the S does the same now, or by the time summer comes on, updates will provide fine tuning.
The Roadster most definitely does balance with a Standard charge. However, it does something more after a Range charge. I've been told this by various Rangers, and have seen clear evidence myself that they are correct. Exactly what "more" is done is not clear.
Nor is it clear that the Model S works the same way.
Besides what other folks have said, in the summer it's probably a good idea to start the charge a few hours after the day's drive and end it a few hours before the next day's drive. My hypothesis is that Tesla's BMS will keep the battery within the proper temperatures even if you don't do this, but it will use more power to do so because there will be more heat to get rid of.
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