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Discussion Starter · #1 · (Edited)
I know this is a rather silly question and please do forgive my ignorance but after scouring the internet I just can't seem to find a straight answer anywhere.

We all know that we should seldom charge the car to 100% and on the rare occasions when we do (for road trips, battery balancing etc.), we're told to never leave it at 100% for too long. But how long is 'too long'? A couple of hours? 6 hours? A day?

The reason why I'm asking is because we're planning to do a trip soon so I'm probably going to charge the car to 100% (also to balance the batteries as I've never charged it to 100% before in the 1 and a half years of owning it). However, because I'm on Octopus Go, the off peak rates end at 4:30am. So assuming the charge to 100% finishes dead on 4:30am and we're not setting off until about mid-day, it'll be sitting at 100% charge for a good 7 hours. Now don't get me wrong, I'm not suggesting this will destroy the battery in any way as it would take a lot of these 100% charges before we would notice any degradation, but I'm still somewhat paranoid.

The only answers that I can find from other forums are the typical, "Ah don't worry about it, just enjoy the car, the battery will be fine!", which doesn't really answer the question. No one seems to know. What are your thoughts? What's the longest you've had it at 100%?
 

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I know this is a rather silly question and please do forgive my ignorance but after scouring the internet I just can't seem to find a straight answer anywhere.

We all know that we should seldom charge the car to 100% and on the rare occasions when we do (for road trips, battery balancing etc.), we're told to never leave it at 100% for too long. But how long is 'too long'? A couple of hours? 6 hours? A day?

The reason why I'm asking is because we're planning to do a trip soon so I'm probably going to charge the car to 100% (also to balance the batteries as I've never charged it to 100% before in the 1 and a half years of owning it). However, because I'm on Octopus Go, the off peak rates end at 4:30am. So assuming the charge to 100% finishes dead on 4:30am and we're not setting off until about mid-day, it'll be sitting at 100% charge for a good 7 hours. Now don't get me wrong, I'm not suggesting this will destroy the battery in any way as it would take a lot of these 100% charges before we would notice any degradation, but I'm still somewhat paranoid.

The only answers that I can find from other forums are the typical, "Ah don't worry about it, just enjoy the car, the battery will be fine!", which doesn't really answer the question. No one seems to know. What are your thoughts? What's the longest you've had it at 100%?
That's just it. No one really knows but there's this internet myth that gets bandied about and like a Chinese whisper, gets distorted until it becomes lore. The BMS will sort it out for you. That's what it's designed to do. That's why you get a longer battery warranty than the car.

I've left my car plugged in and fully charged for more than a week and, believe it or not... it didn't blow up or die or lose some of its power. I have to be cautious here because there will now be a string of commentators who will start preaching how I am being silly for doing this because, in the long run, I will be degrading my battery unnecessarily and blah, blah, blah. I am confident that the battery will outlive the car. Try searching for how long it takes for dendrites to form. The BMS takes care of the battery health.

It's like watching a soap opera sometimes reading the preaching of internet myths as though they are gospel. The timid EV owner who has a mental health problem due to anxiety because they have left their car fully charged for a few hours. The EVangelist who preaches degradation and failure if you top up to 100% more than once a month.

Life is too short to worry about some of the crap that gets spouted on the internet. A bit like the anti-vax conspiracy mob, natural selection will eventually thin them out.
 

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I think the answer is in days not hours - advice about other Lithium Ion batteries seems to mention timescales in days not hours. But as you say no one really knows - just follow good battery charging habits and don't worry too much about it when you have to charge to 100%.
 

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I know this is a rather silly question and please do forgive my ignorance but after scouring the internet I just can't seem to find a straight answer anywhere.
And you will not find a straight answer, since most of it is utter nonsense made up on the spot.

Charge the car to 100% and stop worrying, by not charging it to 100% for the last 1.5 years you've probably done more harm than good, as the BMS no longer knows what the top of the battery looks like.
 

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As above, there is loads of total crap about. I've (accidentally) kept a battery pack (my motorcycle battery, not a car) on charge to 100% for about 7 months (I forgot I'd left it charging). Nothing happened, no battery capacity was lost, it's just the same now as it was before. The BMS just shut down at 100% and the battery sat there, fat dumb and happy, with nothing bad happening.

Now if I had charged it to 100%, then discharged it to 0%, every day for those 7 months then it would undoubtedly have hammered the battery cycle life, and some capacity would have been lost. However, even with the relatively low range of the bike that would have meant riding about 19,000 miles over that 7 months, and as it was winter that would have been extremely unlikely.
 

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Stop worrying, battery longevity is mainly a function of temperature, if you live in Texas maybe you need to be careful but if you are in Essex find something else to worry about. OP you haven't said what car it is and that matters a bit. BMW recommends that the I3 is kept at 100% (indicated not real) and there is no evidence that this causes any damage at all. Tesla recommends staying below 80% (again this is the indicated figure not what the cells actually have) but the evidence for significant degradation is pretty thin on the ground.
 

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Discussion Starter · #7 ·
I'm referring to the Tesla Model 3 (LR), which I thought would have been obvious as we're in the Tesla Model 3 forum :p

But thanks for the response. Just hearing some anecdotes from others who have charged to 100% and even kept it at that level for days/weeks without any degradation puts my mind at ease. I don't plan on doing that myself as I'll be setting off on my trip within 12 hours of charge but always good to know anyway.

On a slightly different note, this line made me chuckle :D

Life is too short to worry about some of the crap that gets spouted on the internet. A bit like the anti-vax conspiracy mob, natural selection will eventually thin them out.
 

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The following is my understanding and my opinions:

Your car's battery doesn't need to be charged to 100% to balance the cells. For this you should leave the car overnight on different SoC, low and high, observing the good practice numbers (20-80, 10-90, whichever you feel comfortable with).

Before a long trip I charge to 90% or 95%, I also never charged the battery to 100%.
 

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When going on a long trip and needing 100% charge, I charge at the cheap rate to about 90% and then top off later so that 100% is reached just before departure.
It probably doesn't matter that much but for the sake of 5kWh or so at the full price it makes no sense to worry in either direction.
 

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I'm sure its probably fine, but like with many things, you get people fretting (and lack of concrete information to help with the decision)

I have a trip to pick up my son from Uni on Sunday and need to be at 100%. Last time I charged to 90 the night before with Octopus Go, then in the morning manually turned on the charger to top it up about 90 mins before I left.

This time I'm tempted to just whack it up to 100% on Saturday night and leave it to it.
 

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Whilst this doesn't directly answer your question it's about as close to an answer I can find from Tesla themselves

Range Tips
 

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I know this is a rather silly question and please do forgive my ignorance but after scouring the internet I just can't seem to find a straight answer anywhere.

We all know that we should seldom charge the car to 100% and on the rare occasions when we do (for road trips, battery balancing etc.), we're told to never leave it at 100% for too long. But how long is 'too long'? A couple of hours? 6 hours? A day?

The reason why I'm asking is because we're planning to do a trip soon so I'm probably going to charge the car to 100% (also to balance the batteries as I've never charged it to 100% before in the 1 and a half years of owning it). However, because I'm on Octopus Go, the off peak rates end at 4:30am. So assuming the charge to 100% finishes dead on 4:30am and we're not setting off until about mid-day, it'll be sitting at 100% charge for a good 7 hours. Now don't get me wrong, I'm not suggesting this will destroy the battery in any way as it would take a lot of these 100% charges before we would notice any degradation, but I'm still somewhat paranoid.

The only answers that I can find from other forums are the typical, "Ah don't worry about it, just enjoy the car, the battery will be fine!", which doesn't really answer the question. No one seems to know. What are your thoughts? What's the longest you've had it at 100%?
I don't think there isn't an answer to 'How long is too long?'. I suspect it's just a matter of keeping the cumulative number of hours the car sits at 100% as low as possible without making life hard for yourself.

Lithium Ion batteries degrade slowly over time. This happens faster if battery is hot and it happens faster at high states of charge.

A 2 year old battery that has spent 6 months at 100% charge will have more degradation than one that has just spent a few hours at 100%.
 

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I don't think there isn't an answer to 'How long is too long?'. I suspect it's just a matter of keeping the cumulative number of hours the car sits at 100% as low as possible without making life hard for yourself.

Lithium Ion batteries degrade slowly over time. This happens faster if battery is hot and it happens faster at high states of charge.

A 2 year old battery that has spent 6 months at 100% charge will have more degradation than one that has just spent a few hours at 100%.
Can you please point me to a definitive study where this is defined, perhaps with statistics to show how much degradation occurs to a BMS managed LiOn EV battery.
 

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I charged my leaf to 100% for 3 years and it lost 2% over that time.. not enough to worry about and I doubt if it would have been lower if I'd stressed about it.. I'd just have had more grey hairs.

Default in the tesla app is 90% and I'm content with that. Tesla knows best.. haven't seen any significant range loss in the last year.. not that I'm measuring it - I'm firmly in the 'enjoy the car' camp.
 

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I always charge my Soul to 100% - but haven't seen ANY degradation at all - I've only had it 9m to be fair, but even so, would have expected some if charging to 100% caused damage.
 

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I charged my leaf to 100% for 3 years and it lost 2% over that time.. not enough to worry about and I doubt if it would have been lower if I'd stressed about it.. I'd just have had more grey hairs.

Default in the tesla app is 90% and I'm content with that. Tesla knows best.. haven't seen any significant range loss in the last year.. not that I'm measuring it - I'm firmly in the 'enjoy the car' camp.
We've had two Leafs (Leaves?) from new over the last eight years or so and have always charged each one to 100% once or twice a week at home/as needed. I can't recall exactly what the degradation was in the first, which we kept for 2 1/2 years, but it was minor. The second we've had for a smidge over five years and has dropped a little over 12%, I think - not because of charging to 100% at home but because, I'm convinced, I supercharged the nuts off it. Which the Leaf really doesn't like.

Got a Model 3 on the way as my daily driver and, yes, absolutely, Tesla know best. 90% seems fine by default, but an occasional hit of 100% (either before a very long trip or just to calibrate things) I'm sure will be fine.
 

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August 19 car, never charged above 90%. I try to average a 50% SOC. The car sits on my home charger at 50%. If I estimate my next trip will use 40%, I'll charge to 70% the night before and arrive home at 30% then back to 50% overnight.
 

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That's just it. No one really knows but there's this internet myth that gets bandied about and like a Chinese whisper, gets distorted until it becomes lore. The BMS will sort it out for you. That's what it's designed to do. That's why you get a longer battery warranty than the car.

I've left my car plugged in and fully charged for more than a week and, believe it or not... it didn't blow up or die or lose some of its power. I have to be cautious here because there will now be a string of commentators who will start preaching how I am being silly for doing this because, in the long run, I will be degrading my battery unnecessarily and blah, blah, blah. I am confident that the battery will outlive the car. Try searching for how long it takes for dendrites to form. The BMS takes care of the battery health.

It's like watching a soap opera sometimes reading the preaching of internet myths as though they are gospel. The timid EV owner who has a mental health problem due to anxiety because they have left their car fully charged for a few hours. The EVangelist who preaches degradation and failure if you top up to 100% more than once a month.

Life is too short to worry about some of the crap that gets spouted on the internet. A bit like the anti-vax conspiracy mob, natural selection will eventually thin them out.
Battery degradation is very real and impacts the usability of electric cars. This used to report over 100 miles when fully charged, and as you can see has lost almost half of its capacity (only 7 of 12 capacity bars remain).

145596
 

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Battery degradation is very real and impacts the usability of electric cars. This used to report over 100 miles when fully charged, and as you can see has lost almost half of its capacity (only 7 of 12 capacity bars remain).

View attachment 145596
Agreed, but how much if that degradation is due to charging regime and how much is due to charging cycle caused loss (“normal wear and tear” unrelated to the level the batteries have been charged over their life)?
 
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