Optimum Charging/Use Scenario

[Dubes]

I must say that I am not on board with the idea that OCCASIONAL deep discharging is bad for my battery life.
There is a tweet from Elon saying that going to 5% or less is not a problem. More importantly there are many people claiming that deep discharging is bad without any data. Although I admit data is difficult to find, what I do find seems to show that Elon is correct as long as you plug in after deep discharging.
I believe the incorrect information may just be misinterpretation of data. Here is one graph of Dod (depth of discharge) vs life:
Long Cycle Life Lithium Iron Magnesium Phosphate Battery
Although on first glance it appears "obvious" that deep discharging is bad, this doesn't consider that a deeper discharge delivers more energy per cycle. For instance, these Lithium batteries have 15k cycles at 40% Dod and 5k cycles at 80% Dod. So 80% Dod delivers equivalent of 10k cycles at 40% Dod.
I think the takeaway point is that doubling the Dod for any one discharge is similar to using three small discharges instead of two. This is very different than saying even an occasional deep discharge is very bad for your battery.
So if I have a 300 mile range battery that I typically cycle 70%-30% (120 miles), I might expect about 3000 of these cycles for >300k miles of use. If I happen to use a 90% - 10% cycle for a 240 mile trip, I would use three of my 3000 cycles instead of two.
I believe this is important because when we go on a trip that requires 80% of capacity, we need to decide whether to go 100% - 20%, 90% - 10%, or 70% - 30% with a SC stop. I believe that the first two of these choices is significantly better than SC. We know that frequent SC is discouraged and that SC speed is limited by Tesla after ~300 SC to prevent battery damage. (2x/month for 15 years = 300).
So in my opinion it is best to save those few 300 SCs for long trips (> 80% range), deep cycle for moderate range trips, and keep it plugged in to short cycle whenever possible. Most importantly just enjoy our amazing Tesla's!!

 

[vqiwei]

In normal, non-abusive use, yes, cycles are the main component of wear. But excessive discharge just once easily cuts your available cycles by about 10%. That said, from what I've read in Nick Howe's book, it looks like Tesla SW is doing all it can to prevent excessive discharge.

The other major destructive force is storing at 100% for an extended period (more than 12 hours). That cuts useful cycle life by about 1% (30 cycles given the rated life of the Tesla battery)

That said, in my hobby usage I've found that if I baby the battery, it will last far longer than rated cycle expectations.

great info. what about supercharge?

 

[RedXowner]

Hi, I'm a brand new Tesla owner, and of course I've got the obvious charging questions about the battery. I, like all new Tesla owners, want the batteries to last as long as possible before needing battery replacement. When you buy your car, there is a date on the calendar in the future that you will have to replace your batteries. You don't (and Tesla doesn't) know when this date is, but it is most certainly out there. The question is, are the things the owner can do to move that date to the right, and how much of an effect (large or insignificant) do those optimal best practices move that replacement date to the right? Maybe the answer to even that question is not known. Assuming the answer is best practices will give the owner an extra 6 months to a year of battery life, and the best practices are insignificant and easy to follow, why not do them? I think that's what we all want to know. I understand that LI-ion batteries like a 50-65% charge state. That's where you'd like the car to be most of the time. OK, if that's true, for me, I don't drive a lot on a given day. So if I know I'm only going to be driving 15-20 miles for many days in a row, should I set my max charge to, say, 65%, run about 5% out of it, then plug it in again every single day to get it back up to 65%? Or is it better to charge it to 80 or 90%, run 5% out of it per day, don't charge it at the end of each day, and let it get down to some lower level, say 30%, and then charge it back up to 80 or 90%? And regardless of what I do in these situations, how far is it really moving that date on the calendar to right?

 

[bob_p]

As long as you use Tesla chargers (not 3rd party chargers, especially for fast charging), avoid letting the battery fully discharge, and avoid having the batteries stay below 10% or above 90% for extended periods, then you should be OK.

Tesla's hardware and software is designed to protect the battery packs - so owners shouldn't need to worry about optimizing charging to protect the batteries.

 

[puhiniho]

I asked my DS the same question. He and the manual suggest not going to 0%, 5% might be a good lower value especially if some energy is unavailable when the battery is very cold. Also, the "daily use" level suggests that consistently charging to about to 80% and using full "trip - 100%" only when needed.

I also asked the DS about charging rates. I've always heard that slower the better if you can afford the time, but he could not confirm that. Anyway, my HPWC is set for 64A because it's on an 80A circuit.

Reading this comment got me asking...all you battery gurus, is it better to charge at lower amps than higher amps (exclude supercharger)? Since I charge almost every night, I just plug it in and typically set it to 22a to charge all night. Even though my HPWC goes up to 72a (100a breaker), I don't typically go that high unless I'm in a rush (and it can be a real lifesaver at time).
Anyway, just curious to hear from others?

 

[ShawnA]

Hi Puhiniho,

I am certainly NOT a battery guru...
There are losses that occur while converting AC/DC and voltage conversion while charging before even reaching the battery...
The longer you charge the more time elapses for these losses to accumulate.
It is easier on most equipment to charge at a lower level so heat generation does not accelerate component failure.

If you boosted the charge level to 48 A, you might find a sweet spot that balances the losses
against the thermal stress of charging at maximum (home) rates...

Considering Tesla only offers a 48 Amp charger now (3/2020) in the larger battery cars, they may consider this the sweet spot.

Shawn

 

[RedXowner]

Thanks for the replies. The reason I asked the questions is that Tesla gives owners the options for "how" to charge. The car lets you set the amperage (discussed above) and the charge-to level, and you obviously decide how often to charge. Since the owner is offered these options, I am simply trying to learn if any of these options or combination of options affect the longevity of the battery pack. I learned just recently that a 100-series battery pack replacement goes for about $20K, so I'm not looking forward to doing that, really, ever. So whatever I can do to keep that replacement date pushed off to the right, I'll do. What I've heard and learned is that not going below 5% or 10 or 20 is good for longevity, so I'll obviously try to avoid doing so. And only charging to 75 or 80 for routine daily driving is also good, so that's what I'm doing now. I only plan to charge to 100% for long trips, and only supercharging when I have to. I also heard that letting the car go down to 20% before recharging is better than recharging every single day when the car only needs 10% to get back to 75, but I found myself unpredictably needing more charge than I had one day when I started the day at around 30%, so keeping the car up to at least 50% is probably as low as I want it to get routinely. If there's anything else, blast away. Thanks again.

 

[Bigriver]

I am simply trying to learn if any of these options or combination of options affect the longevity of the battery pack. I learned just recently that a 100-series battery pack replacement goes for about $20K, so I'm not looking forward to doing that, really, ever.

I too initially stewed over battery health and how to be one of those with a battery that remains the healthiest. After 2.5 years with the model X and 1.5 years with the model 3, I’ve learned to chill about it. Tesla has phenomenal battery technology. Elon has tweeted to not worry about a full charge if needed, and it’s really ok to go below 5% if needed. The battery is not as frail as many owners treat it.

If you don’t use the car for many miles but do want to be prepared if it is needed, why not just charge it to 60% or 70% regularly? That is not going to damage anything.

As a side topic to battery HEALTH, tho, is the battery management system, and it can start displaying a lower than real range if the battery is never more fully cycled. Here is an excerpt from an email I received from Tesla. I don’t think this actually needs to be done every few weeks, but I’d do it several times a year if long trips weren’t sometimes taking it outside a narrow daily range. This isn’t really about the health of the battery tho, it’s about their algorithm that calculates the range.

• Range- Are you feeling like you're getting less range than you should? Try running the battery down to 10% and charging it fully to 100% once a week every couple of week to ensure your range is being calculated correctly.

Your concern about having to replace the battery and looking at today’s cost estimates seems a bit misplaced. First, your battery has an 8 year warranty. You couldn’t possibly need to pay for a new battery in that time. Second, battery technology will have advanced so much in 8 years that today’s cost and technology is pretty much irrelevant.

 

[RedXowner]

I too initially stewed over battery health and how to be one of those with a battery that remains the healthiest. After 2.5 years with the model X and 1.5 years with the model 3, I’ve learned to chill about it. Tesla has phenomenal battery technology. Elon has tweeted to not worry about a full charge if needed, and it’s really ok to go below 5% if needed. The battery is not as frail as many owners treat it.

If you don’t use the car for many miles but do want to be prepared if it is needed, why not just charge it to 60% or 70% regularly? That is not going to damage anything.

As a side topic to battery HEALTH, tho, is the battery management system, and it can start displaying a lower than real range if the battery is never more fully cycled. Here is an excerpt from an email I received from Tesla. I don’t think this actually needs to be done every few weeks, but I’d do it several times a year if long trips weren’t sometimes taking it outside a narrow daily range. This isn’t really about the health of the battery tho, it’s about their algorithm that calculates the range.

• Range- Are you feeling like you're getting less range than you should? Try running the battery down to 10% and charging it fully to 100% once a week every couple of week to ensure your range is being calculated correctly.

Your concern about having to replace the battery and looking at today’s cost estimates seems a bit misplaced. First, your battery has an 8 year warranty. You couldn’t possibly need to pay for a new battery in that time. Second, battery technology will have advanced so much in 8 years that today’s cost and technology is pretty much irrelevant.

 

[RedXowner]

Thanks Bigriver. Since I bought my MX from Tesla's Used website, I only have 4.5 more years of warranty - still a lot, but not the full 8 that it had when new. Everything you said makes sense, and I've heard it before anecdotally from others. The more I hear an opinion or idea about the batteries, the more confident I am with it. I guess one of the main things I was wondering about was the amperage. Seems the car always throttles back my charge rate from the available 40 amps at my house to 30 amps. But since the car's highly capable battery charging technology is the thing that's making this change, I should just accept it and let the car charger do its thing. Also understand the difference between the algorithm being accurate and the battery health. Going on a long round trip tomorrow (3 hours each way) that will certainly require SC at least twice total. I'll make sure to be at 90+ before I depart my house and won't be concerned to pull into my garage between 5-10 left.

 

[MrTomP]

Thanks Bigriver. Since I bought my MX from Tesla's Used website, I only have 4.5 more years of warranty - still a lot, but not the full 8 that it had when new. Everything you said makes sense, and I've heard it before anecdotally from others. The more I hear an opinion or idea about the batteries, the more confident I am with it. I guess one of the main things I was wondering about was the amperage. Seems the car always throttles back my charge rate from the available 40 amps at my house to 30 amps. But since the car's highly capable battery charging technology is the thing that's making this change, I should just accept it and let the car charger do its thing. Also understand the difference between the algorithm being accurate and the battery health. Going on a long round trip tomorrow (3 hours each way) that will certainly require SC at least twice total. I'll make sure to be at 90+ before I depart my house and won't be concerned to pull into my garage between 5-10 left.

Just curious, i also bought a used 2016X in February from Tesla and I thought the warranty starts over, where it is a 4 year full warranty and an 8 year battery warranty. From what you mention above, sounds like my battery will expire around the same as my 4 year warranty. I guess I can go back at my purchase agreement to verify.

 

[RedXowner]

Hi MrTomP, from my extensive review of the website, when a car had less than 50K miles, it came with a 4yr, 50K miles warranty (whichevr comes first) on the car and the remaining ORIGINAL battery and drive train warranty which was exactly 8 years from date of original sale when new, which for me was longer than 4 years by about 6 or 7 months. That seemed to be true for every car I saw. If more than 50K miles on the used car, then the warranty was only 2 yrs. I think battery and drive train were same warranty - what was remaining on the original warranty which is all about a date, not mileage.