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What should my ideal charge percentage be?
- Thread starter Al Sherman
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aerodyne
2 of 3 EV's - Defect Free!
FlatSix911
Porsche 918 Hybrid
Agreed - I like the detailed free monthly battery health report they provide.
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JCtx
Member
I was doing between 50 and 70% before, but switched to 60 to 80%. Very few times I have to charge the car two days in a row. My average is about every 3 to 4 days (with a NEMA 14-50). The charge time is about 2 hours, so an hour for every 10% of charge. Is it a good strategy? Thx.
Oh dear, I guess I missed that particular guidance. I have had my car for 6+ years and don't recall seeing that recommendation before. Maybe I missed it, or more likely failed to take it in, among all the various conflicting guidance I have read over those years. I seem to recall most guidance being closer to 80%.
Honestly, I wish there were official Tesla guidance on this stuff, or a consensus among true "experts," if there are such.
I guess I was overly influenced by tesla's early guidance when I bought the car -- Always Be Charging." I've kept mine up around 70% but I have never done a degradation test so I have no idea how well that has worked out....
Sorry, to clarify, "around" the middle point/50% point overall, is optimum for the pack. But that's being "ideal". The middle 30% should be the overall target range to keep the battery within that area regularly
If your daily travels consume 30 percent of the battery, using a middle-30-percent (like from 70 to 40 percent) is better for the battery than always using the top 30 percent.
How to Make Your Lithium-Ion EV or Device Battery Last Longer
Tips on managing your vehicle battery’s temperature, state-of-charge, and the charging and discharging rate to ensure it lasts as long as possible.
When I was commuting daily (pre covid), my commute was 10 miles each way. So I'd typically charge to about 65% each night. One a month I'd let it get down to about 15%, then charge to 85%. Then back to my regularly scheduled 65% max charge at night. But I did keep it plugged in each night, so that the Battery Management System could do its job and to help pre-condition the car on very cold mornings when I'd set the HVAC to warm the cabin before I left.
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The latest data suggests that it's even better to use the bottom 30% rather than using the middle 30%. So go for 50-20% instead of 70-40%.
FlatSix911
Porsche 918 Hybrid
Good summary - thanks for sharing the article.Sorry, to clarify, "around" the middle point/50% point overall, is optimum for the pack. But that's being "ideal". The middle 30% should be the overall target range to keep the battery within that area regularly If your daily travels consume 30 percent of the battery, using a middle-30-percent (like from 70 to 40 percent) is better for the battery than always using the top 30 percent.How to Make Your Lithium-Ion EV or Device Battery Last Longer
Tips on managing your vehicle battery’s temperature, state-of-charge, and the charging and discharging rate to ensure it lasts as long as possible.www.motortrend.com
When I was commuting daily (pre covid), my commute was 10 miles each way. So I'd typically charge to about 65% each night. One a month I'd let it get down to about 15%, then charge to 85%. Then back to my regularly scheduled 65% max charge at night. But I did keep it plugged in each night, so that the Battery Management System could do its job and to help pre-condition the car on very cold mornings when I'd set the HVAC to warm the cabin before I left.
Yes, there is not really any doubt of this.
This knowledge is not really ”new” either.
The ”new thing” might be that there is a lot of forum thruths that just ain’t right.
All research about lithium battery degradation tell us the same thing:
= The lower the SOC the better.
The rumor that low SOC is bad is wrong.
We know that lithium batteries does not degrade from being att very low SOC.
As long as they are kept inside the voltage limit, low SOC is the best.
Teslas 20 / 10% amber/red color on the battery has been wrongly taken as a hint that below 20/10% is bad.
Teslas battery shut down before the voltage is too low. Research also show that going below the min voltage( 2.50v/ cell) does not harm the batteries on most cases. Anyway, Teslas BMS disconnects the battery before this happens.
The 12V battery do not like low SOC, so it might get damaged after the big lithium battery disconnects.
Theres two types of degradation:
Calendar aging and cyclic aging.
Calendar aging comes from time and is driven by [SOC x Temperature x Time]
Reduce any of the three and the degradation from time will reduce.
Calendar aging is by far the dominant part in the first five years of a EV.
The first year calendar aging is between 4 to 10% for most average used Teslas.
Above, if you have an average battery temp of 25C, and Charge to 80% each night but do not drive much the average SOC will be close to 80%. This will degrade the battery with about 5% for 9.6 months, or about 5.5% for the first year. This has nothing to do with degradation due to driving/ charging so this happens regardless of the miles.
We can see that 0% causes the least caöendar aging( still within the minimum voltage) and that hot days with 100% will take a big bite of the capacity.
Driving/ charging causes cyclic aging. Cyclic aging is less the lower SOC we use, so for example on research report using NCA chemistry( as Panasonic use in the Tesla Batteries) found that 10% cycles around 70% did degrade the battery with 10% after 6000 of these small cycles( = 600EFC). On hte other hand, same cycle count and size but around 30% SOC only degraded the battery 2%.
Low SOC during cycles degrade the battery much less.
Small cycles is also much better when it comes to degradation. Charge often.
The charts mostly refer to FCE, Full Equivalent Cycles.
For example, ten 10% cycles is 1 FCE.
If you keep the SOC low, use as small cycles you can tour battery will keep the capacity very long and degrade slower.
I use that technique. I have not lost any range at a 100% charge yet. Of course my battery has degraded a little( some 2.5% or so) during my first 40K km / 25K miles.
FlatSix911
Porsche 918 Hybrid
See item 4... Low State of Charge can corrode the copper current collector in the anode and dissolve transition metals.
Well, to 99.9% certainty or more, this is not a real problem om todays LiB.
There is no science/research reports that show any increased degradation of lithium batteries at low SOC.
There is, though, a lot of ”It is like this“ or “its like that” on the internet that actually is not correct.
The definition of 0% SOC is most often a voltage, like 2.5V/cell for the Panasonic NCA(18650, 2170). Staying not below the minimum voltage is safe. In fact, if you look for research about what happens when you go below it will show that if you go a little below, nothing happens and if you go very low(like discharge to 0V, about 50% of the cells do get damage and 50% do not, so it is unsafe to overdischarge the batteries far below the lower limit. Anyway, Tesla disconnect the battery for the car with the contactors befor going below the lower limit. We can not do any low voltage damage on the lithium battery. (The 12V lead acid battery is sensitive though, and would eventually get discharged after the lithium battery has been disconnected, but that is another story.)
This is the look of a typical calendar aging graph. We clearly can see that 0% will cause the lowest calendar aging, even if the battery is left for a year.
This picture is from this report: ShieldSquare Captcha
There is about 50 or more research reports easy accessible on the net, and more of one asks the authors for not open reports. All, telling us the same thing. This one is also recommended: https://www.researchgate.net/profil...n-Capacity-Fade.pdf?origin=publication_detail
The trick to find, is google.com and search for *calendar aging lithium batteries* or *calendar aging lithium NCA* if being specific for the NCA chemistry that Tesla/Panasonic use.
If you would like to make a lithium battery hold up forever, you should cycle it between 0 and 10% or 10-20% SOC or so.
Se below. It should be quite clear that 10-20% is much better than 40-50 or 60-70%.
Thanks for the info. So plugging in each night is, or is not whats best long term for the battery pack?
Well, how should Iput it…?
Teslas advice is supposed to be easy and also be the same advice for all.
If you adopt a few parts from the research results you already have cut the degradation in half, or more.
While it is possible to be very extreme and reduce the degradation further, in the end you need to decide how far you will take the efforts. Is ot worth having the car standing woth so low SOC that it cant be used if not charged?
If you use low SOC and drive the SOC down each day, so it is low during the night the car can be charged each night.
Small cycles is best which means charge often. ( but charging to 90% every night and using only 10% os not jte best approach).
So you need to decide, but if you charge to 50% every night and drive it down during the day it will average below 50%.
I charge to 55%, use 20-35% each week day depending on the time of the year.
The car stands with 20-35% during the night and get charged innthe morning before next drove to work.
I would not gain anything by not charging every night.
For weekends, I could teoretically leave it at 20-35% all weekend and only charge if I need the car but this would reduce the freedom of movement so I charge to 55% weekend nights as well.
If you drove very little (like 10% or less, there would be an option to not charge every night to redice the average SOC, but it might only be a small win and the effort perhaps doesnt make it worth it?
Picking a charging strategy is like joining a church (or not attending). I'm joining the church of AAKEE, which seems to have the best technical support (I'm an engineer by training). My summary:
I bought from a good friend at 4 years and 85k miles, so longevity is more critical, but some opportunity has been lost. Any benefit to knowing his charging habits? Any benefit to me getting some assessment and monitoring app?
- Set upper charge limit as low as possible to comfortably meet your potential needs for your next drive. Like one might rarely charge to 100%* for a big trip, one might occasionally charge to more than the standard low level for a big local driving day ahead with dog mode and other such needs. I rarely need more than 20-30 miles for my limited driving, but setting to 50% (150 miles) is probably fine. Maybe I should go lower?
- Keep topping if off to the base limit instead of occasionally "exercising" to greater depletion levels. Use the range only when you need it on trips, so it will be there for trips in the long term. Don't waste it with needless exercise.
I bought from a good friend at 4 years and 85k miles, so longevity is more critical, but some opportunity has been lost. Any benefit to knowing his charging habits? Any benefit to me getting some assessment and monitoring app?
Low SOC is good. After four years the calendar aging has a rate of about a fifth of the first year so its less ”sensitive” if you compare the rate.
Low SOC gives low calendar aging but it also reduce the cyclic aging. The same depth of discharge cause much less wear at lower SOC.
So charge to a low SOC and if possible charge ’just before’ will result in a low degradation.
Teslas lowest setting is 50%. I use 55% even if 50% would work most times.
If the charge is performed shortly before the drive and the car has lower SOC before the charging level has minor impact on the calendar aging.
I charge every night, about 0300-0330 makes the charge complete before driving to work.
The battery would stand perhaps 500 or 1000 cycles 100-0% before you have lost 20% from the cycles. Lets say 500. This means that each degrade the battery about 0.04%. You could do 20 a year abd this would cost you 1% capacity. Most times you would not use 100 to 0, so perhaps less loss.
I did about 12 100% charges the first year, 32.000km and still showed full range. I also have around 18% Supercharging.
The ”real range” is slightly lower according to my calculation and a forced ’reset’ of the BMS showed that it seem to be on pair with my estimation(capacity 79.5 kWh).
If keeping the calendar aging very low its possible to do some 100% charges and Supercharging and still have less degradation than most other people.
What have been done before do not really matter, only the ”capacity”.
Monitoring apps etc is only needed on the nerd level. If you find it interresting then it is recomendable. They will not really help in preserving the battery.
We already now the basics:
-Low SOC is best.
-Do not use higher SOC than you need.
- If/when possible, charge late/shortly before driving( keeps average SOC down).
And, not science but common sence:
As the battery will hold up anyway do not go to deep into preserving the battery. Stay on the ”its still fun” level abd enjoy the car
FlatSix911
Porsche 918 Hybrid
Here is my latest monthly battery report from Recurrent Auto... SOC range from 10- 85%.
www.recurrentauto.com
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