Speak EV - Electric Car Forums banner

1 - 20 of 22 Posts

·
Registered
Joined
·
420 Posts
Discussion Starter #1
It is received wisdom that frequent rapid charges and staying at 100% reduces battery life and that rapid charging over 80% is time wasting.

But I have never seen any advice on frequent low rate charging (1.4-7.5 kW) or even keeping the battery at a higher level, say 80% to 95%, having any effect on battery life.

Indeed there is some evidence that V2G use (small, low charges and discharges a number of times a day) actually improves battery life.

Any comments or evidence either way?
 

·
Premium Member
VW ID.3 Worst Edition
Joined
·
4,333 Posts
Be prepared for a raft of conflicting opinions, some based as you say on the early Leaf, and others from renegades like me who charge the car and use it how they like relying on the top buffer, design assumptions and BMS to take care of things.

I have started charging my car to only 70% putting the other 30% in prior to departure via the timer which has the added benefit of pre heating the battery and car for efficiency, but that’s not really for battery longevity reasons.

I do wonder how folks new to EVs will receive all this perceived wisdom, I wouldn’t say it’s a barrier to adoption but it’s something that people probably only hear on forums like this one and pass it on.

I think more and more, manufacturers are taking the issue away by having battery configurations and systems that are a lot more robust.
 

·
Registered
Joined
·
69 Posts
Be prepared for a raft of conflicting opinions, some based as you say on the early Leaf, and others from renegades like me who charge the car and use it how they like relying on the top buffer, design assumptions and BMS to take care of things.

I have started charging my car to only 70% putting the other 30% in prior to departure via the timer which has the added benefit of pre heating the battery and car for efficiency, but that’s not really for battery longevity reasons.

I do wonder how folks new to EVs will receive all this perceived wisdom, I wouldn’t say it’s a barrier to adoption but it’s something that people probably only hear on forums like this one and pass it on.

I think more and more, manufacturers are taking the issue away by having battery configurations and systems that are a lot more robust.
My e-tron encourages you to only charge up to 80% except for long distance journeys, but I think bigger batteries make this issue to away- my real range from 80% with is about 180 miles (or realistically 130, giving room to not panic about finding a charger) , so there’s no need to charge en route or be at 100% unless you’re doing a really big journey.
 

·
Registered
Joined
·
2,281 Posts
Manufacturers are really not interested in promoting product longevity: they build cars to sell. I have owned an i3 for 5 years and I tend to use the inbuilt off peak facility to set a charging time that will give me c.80% with the occasional charge up to 100% for cell balancing.


Standing by for incoming: hard hat time.
 

·
Registered
Joined
·
4,933 Posts
I've just bought an electric outboard for my boat with a couple of batteries. The batteries are lithium-polymer so maybe not directly comparable to car types, but they do contain a BMS.
I noticed in the instructions that for storage they say it is best to maintain about 60% charge.
They also say "If the battery level is larger than 60% for more than ten days without activity, the battery itself will discharge with a small current around 100mA until it reaches the 60% battery level." [Yeah, Chinglish :) ]

So that's a thing.

[Edit: These are 1kWh units, about 42V.]
 

·
I'm not crazy, the attack has begun.
Joined
·
29,916 Posts
It is received wisdom that frequent rapid charges and staying at 100% reduces battery life and that rapid charging over 80% is time wasting.
Let's break this up a little.

'Rapid' charging at 50kW is, in reality, less than 2C charge, and for bigger battery cars even slower. This is really not particularly harmful to a battery using 'conventional' chemistries (NMC/Carbon). Charge rates in the 3C to 5C would tend to degrade over a long time and 7C continuous would tend to degrade more rapidly. This is like charging 30 to 80% in 5 minutes. We don't have that, and 50kW charging hasn't anecdotally accelerated anyone's battery degradation.

Staying at 100% is problematic because the graphite electrode is made to become (electrochemically) very active and it'll slowly degrade the passive surface structure of the cell which (beneficially) forms over repeated charges. So if you charge high and use straight away, it's not going to have a chance to undo that good work from previous charges.

The other reason for generally avoiding high, but also low, states of charge is that the graphite electrode physically expands and shrinks, it is like a sponge. Do it more often to excess and the structure will degrade. So, definitely avoid 100% for days on end, but prefer not to charge to 100% but occasionally is no problem it is designed for it.

(Note; 100% means 'indicated' 100%, the BMS will not allow a charge up to its proper 100% limit, leaving a little buffer/protection.)

But I have never seen any advice on frequent low rate charging (1.4-7.5 kW) or even keeping the battery at a higher level, say 80% to 95%, having any effect on battery life.
That'll be because it doesn't, really.

Indeed there is some evidence that V2G use (small, low charges and discharges a number of times a day) actually improves battery life.
This helps grow the passivated layers on the surface of the electrodes. You can only do this so much, though, and the constant expansion and shrinking of the electrodes will degrade it over time, but if you keep the SOC within 20% or so either side of 50% then it is unlikely you will notice an effect within the battery's warranty period.

If you want the absolute longest lasting battery pack then keep it bouncing either side of 50% on every trip, (Need 10% of battery in a day? Charge to 55% and drop to 45%. Need 60%? Charge to 80% and drop to 30%, like this.) Short <1C charges, often, and staying as close to 50% as you can. The more you deviated from that the more you get degradation. Whether you will ever see the difference is moot, not enough real data there to know. You're more likely to suffer a manufacturing issue with an individual cell before you notice any ageing effect.
 

·
Registered
Joined
·
420 Posts
Discussion Starter #7
Donald, that is all interesting. Your source of information?
 

·
I'm not crazy, the attack has begun.
Joined
·
29,916 Posts
This is from reading a variety of research sources. Not one thing in particular. But once you understand the basics of a Li ion cell it is common sense; Li ions get held in the graphite, so it expands, more ion s, more expansion, more expansion more mechanical stress, those Li ions are trying to react with the rest of the cell but something has to get in the way of the electrons else the electrodes would simply short themselves out and a barrier builds up which stops electrons moving (into/across the cell) but lets Li ions move.
 

·
Registered
BMW 300e 2020 model and Leaf 40kW 2019 model
Joined
·
287 Posts
It is received wisdom that frequent rapid charges and staying at 100% reduces battery life and that rapid charging over 80% is time wasting.

But I have never seen any advice on frequent low rate charging (1.4-7.5 kW) or even keeping the battery at a higher level, say 80% to 95%, having any effect on battery life.

Indeed there is some evidence that V2G use (small, low charges and discharges a number of times a day) actually improves battery life.

Any comments or evidence either way?
I don't think there is any scientific evidence that batteries should NOT be charged to 100% every time you charge. At least the Leaf or BMW manual does NOT state that you should NOT charge the battery to 100% every time if you want to do so. In fact, I think it is the opposite, it is better to charge it to 100% every time than keeping it at lower levels.

I think there is a misunderstanding about this, because some people believe that charging is done through constant current pumping into the car. That is not at all the case. The current is dramatically reduced at the end of the charging which is why it takes forever to get the last ~10% into the battery. I am otherwise convinced that charging to 100% will NOT damage the battery, so I see no point in stopping at lower, unless there is no time to wait for the last drops of juice.

This is the behaviour of slow home wall boxes, but I am sure rapid chargers work the same way, which is why the last percentages takes much longer than the first ~80%. I don't believe rapid chargers or charging to 100% every time can cause any damage.
 

·
Registered
BMW 300e 2020 model and Leaf 40kW 2019 model
Joined
·
287 Posts
Manufacturers are really not interested in promoting product longevity: they build cars to sell. I have owned an i3 for 5 years and I tend to use the inbuilt off peak facility to set a charging time that will give me c.80% with the occasional charge up to 100% for cell balancing.
...on the other hand...
There is a warranty from the manufacturer. The Nissan has 8 years 80%, so why would anyone be interested in keeping the battery level at 80% during the first 8 years...? The way I see it is that it is better to get the maximum out of it while it is new and charge it to 100% all the time. If the capacity will degrade during the first 8 years the I just contact Nissan and demand that they take care of the issue. If I'd ALWAYS charge to 80% (or even worse, do as Donald advice us) then I'd NEVER know if the battery is degraded or not.

The BMW 330e (at least mine) has only 5 years warranty, but still, I apply the same logic. If something is wrong, I want to find out during the warranty period, so I charge even that to 100% every time. It has a range of 48-60km only, so discharging daily almost every day is really not an issue.

Anyway, there is no warning in the manuals of Nissan or BMW about the charging %, so I don't see it as a problem and is highly unlikely that I keep those cars for that long, so I might as well enjoy the maximum capacity.
 

·
Registered
Renault Zoe 50
Joined
·
17,804 Posts
I don't think there is any scientific evidence that batteries should NOT be charged to 100% every time you charge.
There's loads.

The issue is that 100% is not always 100% as indicated by the car. This varies my make and model.

Indeed Teslas will nag you if you charge to 100% more than a few times in a row.
 

·
Registered
Joined
·
25 Posts
Let's break this up a little.

'Rapid' charging at 50kW is, in reality, less than 2C charge, and for bigger battery cars even slower. This is really not particularly harmful to a battery using 'conventional' chemistries (NMC/Carbon). Charge rates in the 3C to 5C would tend to degrade over a long time and 7C continuous would tend to degrade more rapidly. This is like charging 30 to 80% in 5 minutes. We don't have that, and 50kW charging hasn't anecdotally accelerated anyone's battery degradation.

That is very interesting Donald.

Please would you explain what the 2c 7c etc is about? I haven't come across it before.
'Rapid' charging at 50kW is, in reality, less than 2C charge, and for bigger battery cars even slower. This is really not particularly harmful to a battery using 'conventional' chemistries (NMC/Carbon). Charge rates in the 3C to 5C would tend to degrade over a long time and 7C continuous would tend to degrade more rapidly. This is like charging 30 to 80% in 5 minutes.
 

·
Registered
Joined
·
2,281 Posts
Anyway, there is no warning in the manuals of Nissan or BMW about the charging %, so I don't see it as a problem and is highly unlikely that I keep those cars for that long, so I might as well enjoy the maximum capacity.
If you need maximum range, then 100% SOC is obviously needed. Conversely, if you drive a round trip of 20 miles each day in an EV with a 180 mile range then I do not follow the logic of charging the car to 100% each night. It is not as if charging to 100% each night increases the maximum range. It‘s a bit like taking an ICE to a garage each day to top up the fuel tank.

Not that my view matters. How you choose to look after your EV battery is a matter for you.
 

·
Registered
BMW 300e 2020 model and Leaf 40kW 2019 model
Joined
·
287 Posts
If you need maximum range, then 100% SOC is obviously needed. Conversely, if you drive a round trip of 20 miles each day in an EV with a 180 mile range then I do not follow the logic of charging the car to 100% each night. It is not as if charging to 100% each night increases the maximum range. It‘s a bit like taking an ICE to a garage each day to top up the fuel tank.

Not that my view matters. How you choose to look after your EV battery is a matter for you.
Of course, you can do that if you know you only need to drive those short trips, but if you drive a short trip one day and an unplanned long the next, and you never know the trip length next time it is best to keep it topped up. This not the same with an ICE, even if I park with just a few liters in the tank and suddenly must take a longer trip I just stop at the next petrol station for a few minutes and fill it to the maximum so that I can safely take my long trip. With an EV this is not an option, not even with fast charging, and not even if you are happy with 80%. Our EV is used for random length trips due to the type of work my wife does, but I am just and ordinary office rat, so most of the days I take the same trip. On the other hand, my battery is exactly what I need for my daily trip, so it is totally flat when I get home and gets charged to max every time.

BTW, I am not an idiot, I know charging to 100% each night does NOT increase the maximum range, but it keeps the maximum range at maximum, and it isn't reducing the life span of the battery, at least unless you drive a Tesla. :)
 

·
Registered
Joined
·
2,281 Posts
BTW, I am not an idiot, I know charging to 100% each night does NOT increase the maximum range, but it keeps the maximum range at maximum, and it isn't reducing the life span of the battery, at least unless you drive a Tesla. :)
I am not accusing you of being an idiot; however, I do dispute the assertion in your posts that charging has no affect on the lifespan of an EV battery. The fact that you are seeing 100% does not mean that the hidden % headroom is not falling over time. It is worth pointing out that the warranty on an i3 battery over 3 years is based on the usable SOC not on the full capacity of the battery (Max capacity of an i3 120Ah is 42.2kWhs: usable capacity is 37.9 kWhs).

It is logical to assume that second and third owners of an EV will notice the effect of battery degradation in terms of reduced range. There is considerable scientific evidence - outwith manufacturers’ manuals- that shows that EV battery life can be protected to a degree by not allowing the state of charge to fall below 20% and only charging up to 90% - with the caveat that EVs like the i3 need to be charged up to 100% periodically for cell balancing purposes. If you have any scientific evidence that counters what I have read over the past 5 years, then I would be very interested in reading it.

Typical of informed opinion:

 

·
Registered
Joined
·
296 Posts
Sorry I haven't mastered the Quotation business
...or editing it would seem ?

The C notation is relating the charge rate to the capacity of the battery. A 50kWh battery charging at 50kW is said to be charging at 1C. 100kW would be 2C. 350kW would be 7C.
 

·
Registered
BMW 300e 2020 model and Leaf 40kW 2019 model
Joined
·
287 Posts
I am not accusing you of being an idiot; however, I do dispute the assertion in your posts that charging has no affect on the lifespan of an EV battery. The fact that you are seeing 100% does not mean that the hidden % headroom is not falling over time. It is worth pointing out that the warranty on an i3 battery over 3 years is based on the usable SOC not on the full capacity of the battery (Max capacity of an i3 120Ah is 42.2kWhs: usable capacity is 37.9 kWhs).

It is logical to assume that second and third owners of an EV will notice the effect of battery degradation in terms of reduced range. There is considerable scientific evidence - outwith manufacturers’ manuals- that shows that EV battery life can be protected to a degree by not allowing the state of charge to fall below 20% and only charging up to 90% - with the caveat that EVs like the i3 need to be charged up to 100% periodically for cell balancing purposes. If you have any scientific evidence that counters what I have read over the past 5 years, then I would be very interested in reading it.
I don't actually question any of that. My point is: Let time show how my charging habits affects my batteries, let manufacturers warranty take care of the problem if it causes a problem. I really don't believe it will have any significant negative effect, but if it has, then so be it. I mean, what's the point of buying a high performance car and driving it like if it was a slow and low performing one...? Also, if you care about the second hand value of your car then perhaps you bought the wrong car. I don't mean you should not be careful or should abuse it or anything like that, but why pay for something you don't use or worry that it will reduce the second hand value of it if you do? I also believe that many other things can cause far worse capacity degradation, which people seem to ignore, or can't do much about. Even second hand value of a car may drop dramatically caused by something else, like a minor accident, which is totally out of your control. So, adding all those things, I figure I'll worry about the battery when it is time, and if it is dropping capacity it will be time to get a new car anyway. So far, after more than a year's driving with the Leaf, the real capacity is still the same as it was when it was new.

Also, I don't know how you checked your maximum and usable capacity. My BMW has a 12kWh battery. When I totally empty the battery (technically zero percent isn't zero at all, I can't discharge to exactly 0.00%, that's prevented by the car) and electric driving is no longer possible and then connect it to my wall box, the car will suck over 12kWh out of my charger. This has been checked several times. So, in my case I guess the usable capacity is 12kWh as well as the maximum capacity, which is 12kWh according to BMW. Yes, there are some losses in the charging circuit also, but I think that's pretty low. Or am I missing something?
 

·
Registered
Joined
·
2,281 Posts
Also, I don't know how you checked your maximum and usable capacity.
BMW i3 120 Ah and various other sources including the handbook.

Good battery husbandry doesn’t stop you using the car to its full potential. As I said, the battery warranty doesn’t kick in until the battery is below 70% of the usable SOC which is a nearly a loss of 38% of the total battery capacity when new. Time to move on - me thinks.
 

·
Registered
Kia Soul EV 2020
Joined
·
106 Posts
If you want the absolute longest lasting battery pack then keep it bouncing either side of 50% on every trip, (Need 10% of battery in a day? Charge to 55% and drop to 45%. Need 60%? Charge to 80% and drop to 30%, like this.) Short <1C charges, often, and staying as close to 50% as you can. The more you deviated from that the more you get degradation. Whether you will ever see the difference is moot, not enough real data there to know. You're more likely to suffer a manufacturing issue with an individual cell before you notice any ageing effect.
This is my understanding as well.
I would add that high battery temperatures are associated with a much greater loss of capacity. This is mostly in hot desert climates where it is wise to park under sun shades.
Repeated fast acceleration and deceleration can also dump a lot of heat into a battery.

However the newest battery chemistries that use additives that are either more resistant to the expansion and contraction or more able to absorb the expansion and contraction are much more forgiving of faster charge rates.

I would expect that the smaller batteries of a PHEV will have proportionately a much higher buffer that prevents the user fully charging or fully discharging, telling you it is full at 80% and empty at 20%
See my video at
and a list of information sources in the description.
 
1 - 20 of 22 Posts
Top