Best way to charge for battery health?

[Dragon]

Tesla recommends plugging it in every night so that is what I do. If that was detrimental to the battery, they probably wouldn't recommend it.

Most probably you could optimize the charging by plugging it in and taking consideration of a lot of parameters (ambient temperature, battery temperature, state of charge, driving needs next day, etc.). But is it worth the effort? If you do that for 5 years just to have 5-10 miles more on your ideal range, probably not.

 

[dsm363]

That's kind of how I look at it too. I'm sure it's possible to outsmart Tesla's engineers but I'd imagine the savings will be very small as you said. It also takes one of the EV advantages away which is leaving home with a full 'tank' each day, even if you rarely need it.

 

[vfx]

... I'm sure it's possible to outsmart Tesla's engineers ....

Hmmm....

 

[dsm363]

Hmmm....

I meant more in the theoretical sense. If you took all factors into account you might be able to come up with a charge method that was slightly better than simply plugging in every night but I doubt it and it probably wouldn't be worth all the effort to save a very small change in ideal miles over 5+ years. It's safer and easier to simply plug in each night.

I didn't mean to imply that the Tesla engineers weren't doing an amazing job. I think the Roadster has been great and the Model S looks to be even better.

 

[Raffy.Roma]

The cathode in Li ion batteries forms defects (microcracks) due to stress caused by expansion and contraction relative to neighboring materials. It is simply bigger or smaller depending on whether it's charged or discharged. The more you discharge it, the more it changes size. And the more it changes size, the more microcracks it gets. These microscopic cracks lower the battery's capacity. That's one reason why smaller cycles, more often, contribute to longer battery life. That's why you should plug it in every night.

Heat aggravates the microcracking process, so keeping your battery cool contributes to longer battery life. And guess what? Your battery heats up more when used at a lower SOC because it requires more amps to keep your car going 65mph than it does at a higher SOC. That's why you should charge it every night.

Capacity fade also comes from the build-up of non-soluble deposits on the anode and cathode. This chemical process happens faster when the battery is warmer. It also happens faster when at a high SOC. But the process slows to a crawl when you drop the SOC to 80 or 90%, and slows only a tiny bit more at 50%. So if you are going to drive your car, keeping it charged in std mode has less impact on battery life (lower amps, less heat) than driving at a lower SOC. But if you're not going to drive your car for a few days, there are no amps or heat to worry about. That's when Tesla recommends putting it in storage mode, which keeps it at a lower SOC.

end of science lesson.

Can I ask you by taking these precautions after eight years what is the efficiency of the batteries?

 

[wiztecy]

>Can I ask you by taking these precautions after eight years what is the efficiency of the batteries?

hcsharp reported in the battery log thread that he still gets 245 miles in range mode, so I think his charging practice is working for him


>Heat aggravates the microcracking process, so keeping your battery cool contributes to longer battery life.

@hcsharp to contradict that for sake of argument, if you don't need to charge then why charge it? Ignoring the fact of emergency miles... Since heating will result in heating the pack up. So wouldn't be better to not charge it if you don't need to and are over 50%? I think its also key to charge at a lower ambient temperature if possible.

I don't want the SOCs to be sitting higher than 50% with nothing to do (if you know you're not driving the roadster til the morning). So for me I have the Roadster begin its charge so that its completed 1 hour before I leave for work. The one hour gives time for the pack to equalize and cool. Anytime you can allow the pack to cool is a good thing. Then I drive 35 miles to work, for which I pull the SOC down from 185 ideal miles to 150 (81% SOC). The roadster sits unplugged all day, I then commute back home another 35 miles and my ideal miles is at 115 miles (62% SOC). I then plug the roadster, where charge is not initiated until the next morning, in where the cycle starts again where my charge initiates 1hr before I need to depart for work. Over the weekend I don't do too much driving since I live in Santa Cruz and its a resort for me, beaches, bike rides, sun and kayaking in the ocean I leave the roadster unplugged typically over the weekend holding the 60-62% SOC. So my working SOC is between 60% and 81% give or take a few %'s A SOC range the battery pack should like. The one thing I would need to do every so often is to rebalance / equalize the battery pack. The best way to do this is to leave it sitting in Standard Mode for a long duration. If you're going on a trip for a week it is most likely adventurous to use this down time of the EV to equalize. I'd let it sit the week in Std. mode. I was told the battery pack begins this equalization process of the battery pack whenever the SOC is over 80%.

I know the LiPo battery packs tested in consumer electronics favor the 50% SOC in longevity tests I've seen and reviewed with a battery engineer I work with (who's also an EV enthusiast).

 

[Doug_G]

The thing about leaving the battery at lower SOC is that the cell voltage slumps a bit. That means that the car has to draw more current to maintain the same power level, which would mean more heating and stress on the battery. So storing the car at lower SOC is better for the battery, but operating the car at lower SOC is not.

 

[wiztecy]

Thanks Doug and for the background on the battery science technology Henry. Makes sense and very good points to keep in mind. Another thing to consider is AMPs to charge. I believe Tom did an analysis on what Amps are the most efficient to charge at and his curves showed 30Amps ( I need to revisit it if that was the exact Amps, I believe so). Any lower and its inefficient in terms of cost to push the amps across the line. I believe above 30 Amps you start building up heat and heating up the battery packs more than necessary. When I charged at Tesla down in Santa Row they had the 70amp quick charger. I wasn't in a hurry and my charge not too low so I dialed it down to 30Amps in the Roadster.

 

[Raffy.Roma]

>Can I ask you by taking these precautions after eight years what is the efficiency of the batteries?

hcsharp reported in the battery log thread that he still gets 245 miles in range mode, so I think his charging practice is working for him


>Heat aggravates the microcracking process, so keeping your battery cool contributes to longer battery life.

@hcsharp to contradict that for sake of argument, if you don't need to charge then why charge it? Ignoring the fact of emergency miles... Since heating will result in heating the pack up. So wouldn't be better to not charge it if you don't need to and are over 50%? I think its also key to charge at a lower ambient temperature if possible.

I don't want the SOCs to be sitting higher than 50% with nothing to do (if you know you're not driving the roadster til the morning). So for me I have the Roadster begin its charge so that its completed 1 hour before I leave for work. The one hour gives time for the pack to equalize and cool. Anytime you can allow the pack to cool is a good thing. Then I drive 35 miles to work, for which I pull the SOC down from 185 ideal miles to 150 (81% SOC). The roadster sits unplugged all day, I then commute back home another 35 miles and my ideal miles is at 115 miles (62% SOC). I then plug the roadster, where charge is not initiated until the next morning, in where the cycle starts again where my charge initiates 1hr before I need to depart for work. Over the weekend I don't do too much driving since I live in Santa Cruz and its a resort for me, beaches, bike rides, sun and kayaking in the ocean I leave the roadster unplugged typically over the weekend holding the 60-62% SOC. So my working SOC is between 60% and 81% give or take a few %'s A SOC range the battery pack should like. The one thing I would need to do every so often is to rebalance / equalize the battery pack. The best way to do this is to leave it sitting in Standard Mode for a long duration. If you're going on a trip for a week it is most likely adventurous to use this down time of the EV to equalize. I'd let it sit the week in Std. mode. I was told the battery pack begins this equalization process of the battery pack whenever the SOC is over 80%.

I know the LiPo battery packs tested in consumer electronics favor the 50% SOC in longevity tests I've seen and reviewed with a battery engineer I work with (who's also an EV enthusiast).

Does it mean that by treating carefully the batteries of a Tesla Model you could still have an efficiency of almost 100% after eight years?

 

[wiztecy]

There's the factor of time that batteries have a constant shelf life. But it does mean your battery should be more reliable and healthier if you understand the battery technology as well as the physical and electrical principals that are tied to it. The battery logs research is a big part of this and I encourage all to participate. I know every time I stop at Tesla to have anything done they pull my logs. I'm sure they're doing the same and much more analysis on this data as we are to understand battery and charging characteristics based on multiple variables.

 

[spleen]

Thanks Doug and for the background on the battery science technology Henry. Makes sense and very good points to keep in mind. Another thing to consider is AMPs to charge. I believe Tom did an analysis on what Amps are the most efficient to charge at and his curves showed 30Amps ( I need to revisit it if that was the exact Amps, I believe so). Any lower and its inefficient in terms of cost to push the amps across the line. I believe above 30 Amps you start building up heat and heating up the battery packs more than necessary. When I charged at Tesla down in Santa Row they had the 70amp quick charger. I wasn't in a hurry and my charge not too low so I dialed it down to 30Amps in the Roadster.

Think it was 40 amps, based on what I saw in Tom's blog.

Tesla Roadster Charging Rates and Efficiency - Tom Saxton's Blog

 

[hcsharp]

...
hcsharp reported in the battery log thread that he still gets 245 miles in range mode, so I think his charging practice is working for him

Actually it varies from 245 to 247 miles in the summer with 246 being the most common. It's been driven daily for over 14 months approaching 13k mi. But these numbers assume that Tesla's algorithm for calculating the ideal miles is accurate. They've adjusted it a few times in the software. I find the latest revision to be fairly accurate but it might be slightly optimistic.

>Heat aggravates the microcracking process, so keeping your battery cool contributes to longer battery life.

@hcsharp to contradict that for sake of argument, if you don't need to charge then why charge it? Ignoring the fact of emergency miles... Since heating will result in heating the pack up. So wouldn't be better to not charge it if you don't need to and are over 50%? I think its also key to charge at a lower ambient temperature if possible.

You didn't contradict what I said. And in fact you answered the question yourself with your comment about temperature. What you need to keep in mind is that storing the battery at 85 or 90% SOC is only slightly worse than storing at 50% SOC. A far bigger factor is storage temperature.

The problem with your theory that it's better to get home and wait before charging is that a long-ish commute like you have will warm your battery up, especially at freeway speeds. Immediately charging will kick on the roadster's thermal management system and cool the battery down during the first few minutes of charging. That is especially true if charging at very low amperage. That will be much better than letting it hot-soak for several hours. The ideal behavior would be to get home and charge at 12 or 16A for about 30 - 45 minutes to cool your battery off. Then charge as you normally would in the middle of the night at 32 or 40A. That's why I installed a button on my DIY EVSE that, when pressed, will charge the car for 40 min at 16A, then stop, and resume charging at the normal time and amps. If I get home on a warm day, I plug in and press that button. You can do the same with a Tattler if you don't want to build your own HPC.

I don't take credit for this idea. It really belongs to Scott451 and others who developed log parsers. Scott noticed that his roadster would hot-soak until he started charging. One of the best reasons to get a Tattler or OVMS is to help manage your battery temperature and SOC for maximum longevity.

I don't want the SOCs to be sitting higher than 50% with nothing to do (if you know you're not driving the roadster til the morning). ...

True, except that I'd much rather have it sitting at 90% SOC if it's at a lower temp, even if only a couple of degrees lower.

Does it mean that by treating carefully the batteries of a Tesla Model you could still have an efficiency of almost 100% after eight years?

Are you asking about efficiency or capacity? Very little is known about efficiency changes over time independent of capacity. As for capacity, near 100% would be unrealistic in 8 years. The fact that many Roadster owners didn't lose enough to count in the first year or two doesn't mean you can extrapolate from that what will happen in 8 yrs. There's a lot of evidence that the Roadster battery will degrade faster with age, just the opposite of your laptop. See the discussion elsewhere about the failure runaway theory. The best way to prevent that is to keep your battery charged and balanced. And cool

 

[strider]

Thanks Doug and for the background on the battery science technology Henry. Makes sense and very good points to keep in mind. Another thing to consider is AMPs to charge. I believe Tom did an analysis on what Amps are the most efficient to charge at and his curves showed 30Amps ( I need to revisit it if that was the exact Amps, I believe so). Any lower and its inefficient in terms of cost to push the amps across the line. I believe above 30 Amps you start building up heat and heating up the battery packs more than necessary. When I charged at Tesla down in Santa Row they had the 70amp quick charger. I wasn't in a hurry and my charge not too low so I dialed it down to 30Amps in the Roadster.

Keep in mind that Tom's research had nothing to do w/ battery health. It looked purely at the most efficient charging rate - where the least amount of energy from the wall is lost due overhead. I know that's what you said in your post but since this is a thread about battery health, I didn't want someone to extrapolate Tom's efficiency research into the realm of battery health.

 

[PRJIM]

I believe the plug-it in always mantra is due to Tesla not wanting to be liable-or bad press- if an owner forgets the plug in the vehicle (ala bricking story). By preaching plug it in always, it helps avoid customer confusion. I have a friend who owns a roadster and only plugs in his car once the range is <90 Miles. He still gets 189 miles with 23,000 miles on the odo. There are certain circumstances where plugging it in is probably not very helpful. If it is very hot, it is not particularly helpful to have a high SOC or to charge your vehicle.

 

[wiztecy]

Lots of good points bought up in this thread, I now feel better educated which is always good Thanks Strider for the clarification, would be nice to see a mapping to charge amps to battery health.

Also a very good point hcsharp pointed out using the thermal management of the Roadster to cool the pack down after long drives and hot days. I don't see my battery temp really move above the 2nd block. It always stays there, ambient (60-75 degrees F) and higher. If it gets over 90 degrees and I'm doing a long drive or sprinted the car it will move up but not much. Happy with that. I really wish there were numbers and real temps though, that'd be way more useful for temps and the state of the components.

 

[strider]

Lots of good points bought up in this thread, I now feel better educated which is always good Thanks Strider for the clarification, would be nice to see a mapping to charge amps to battery health.

Also a very good point hcsharp pointed out using the thermal management of the Roadster to cool the pack down after long drives and hot days. I don't see my battery temp really move above the 2nd block. It always stays there, ambient (60-75 degrees F) and higher. If it gets over 90 degrees and I'm doing a long drive or sprinted the car it will move up but not much. Happy with that. I really wish there were numbers and real temps though, that'd be way more useful for temps and the state of the components.

That kind of data is only going to come with time. I'm sure Tesla has done a bunch of simulations but ask Nissan how well that's going for them. There simply isn't a replacement for actual data. That's why we should all support Rich's study. From that hopefully we (and the OEMs) can learn how best to care for batteries in this application.

 

[Botbldr45]

With a Tattler what would be a good cooldown target temp for temp management of battery??? My battery sits at around 30 to 36C.... is that too hot???

 

[Doug_G]

With a Tattler what would be a good cooldown target temp for temp management of battery??? My battery sits at around 30 to 36C.... is that too hot???

The car's cooling system tries hard to keep the battery under 40C. I would think that is an upper limit, and it's better not to have it sitting that high while parked. It's not unusual for mine to be close to 40C by the time I get home, due to a combination of driving and sitting in the sun all day.

Probably an ideal temperature would be 20C; however, that's often well below garage ambient in summer. That said, you can cool past ambient and it takes a long time to soak back. Then again cooling takes power. My compromise has been to set the target for 25C, and leave the time limit at 45 minutes (I think that's the default). If it's a hot day it might end up at 30C to 32C after 45 minutes, which is better than sitting at 40C. At 2 AM full charging starts and that typically cools it down some more.

 

[Botbldr45]

Outstanding! Set the Tattler and 992 is cooling as I type. Maryland summer is much hotter than normal ......no Global Warming right!! This is monumental for me ... First time the pack has cooled to under 35C all summer! Wish I had picked up this info last year. Better late than never

 

[daniel]

... The problem with your theory that it's better to get home and wait before charging is that a long-ish commute like you have will warm your battery up, especially at freeway speeds. Immediately charging will kick on the roadster's thermal management system and cool the battery down during the first few minutes of charging...

If the Roadster does not cool the battery pack until charging begins, then why is there a very loud whirrrring sound when I shut off my car after driving hard or on a hot day? I figured that's the car cooling the batteries.

BTW, any talk about X miles driven and Y ideal range remaining needs to be seen in the context of the age of the car. We won't know what the battery can do at 8 years of age until we have batteries that are 8 years old. I doubt that we can really extrapolate from a one- or two-year-old car. When some high-mileage cars are five years old I think we'll just begin to get an inkling.

One of the reasons I chose the Roadster is that at 50% battery capacity I'll still have more range than I need. I'm betting I'll be too old to drive before that happens. I think it's poor planning to buy an EV that has only slightly over the range you need on a regular basis.