Can I limit charging to 80% and if so how?

[EVsince2016]

It is strongly recommended on all EVs to maintain the battery at between 20% & 80% to maintain a longer life with less degradation by all manufacturers.

MG recommend charging to 100% to do a balancing charge once a month.

You only charge to 100% before a long trip and run down to a low % if you have to.

I spoke to an expert on EVs yesterday who drives his MG5 250+ miles per day on average and he often charges up to 90% on a rapid but no more and only when he's having a break as otherwise charging is too slow.

That's it.

 

[Ozzie1989]

I might be missing something, but doesn't the BMS take care of this already? The % indicated on the dash to the driver is not the full battery capacity, it's the percentage of the usable capacity...which is around 93% of the total capacity according to EV database. (Almost identical for LR and SR).

Yes, this is higher than 80% but I'd like to think that the manufacturers (of the car, battery and battery management system) have made sure this is the optimal balance of range and battery durability.

I think everyone gets confused between rapid DC charging and slower AC charging. I've done lots of research and can't find a single manufacturer who specifies their EVs are only charged to 80% regularly on AC. That's why I asked the OP where he got this information from in relation to the MG5...

Lots of people on lots of forums state this, but I haven't seen the evidence yet (for AC charging).

I am still awaiting my MG5 but a colleague has a Kona I think, he's got it on a 4 year lease which is due up soon. He's charged it to 100% every night at home and reckons he's lost about 5 miles charge over the 3.5 years he's had it. Does between 30 and 200 miles per day most work days, and around 130 miles each weekend so he's put a fair mileage on it. Second hand info but a real life example.

 

[Petriix]

I think everyone gets confused between rapid DC charging and slower AC charging. I've done lots of research and can't find a single manufacturer who specifies their EVs are only charged to 80% regularly on AC. That's why I asked the OP where he got this information from in relation to the MG5...

Lots of people on lots of forums state this, but I haven't seen the evidence yet (for AC charging).

I am still awaiting my MG5 but a colleague has a Kona I think, he's got it on a 4 year lease which is due up soon. He's charged it to 100% every night at home and reckons he's lost about 5 miles charge over the 3.5 years he's had it. Does between 30 and 200 miles per day most work days, and around 130 miles each weekend so he's put a fair mileage on it. Second hand info but a real life example.

There's lots of evidence. Just Google 'lithium ion calendar degradation state of charge'. It's about how long the battery spends fully charged.

 

[iainfm]

There's lots of evidence. Just Google 'lithium ion calendar degradation state of charge'. It's about how long the battery spends fully charged.

Which goes back to my point that an EV showing as fully charged at 100% has not got 100% charged batteries. On the MG5, they're no more than 93% charged.

Edit: Nor is a 'flat' HV battery showing 0% charge actually 'empty'. It will have some charge remaining to prevent the degradation of the cells caused when they're absolutely flat.

The worst thing you can do to LiOn cells is pass current through them in the opposite direction, which is what happens with some cells in series go completely flat - the ones still containing the angry pixies will pass a reverse charge/voltage through/across them which absolutely ruins them.

This is usually really noticeable in things like cordless electric drills. If you use them until they're nearly flat you'll probably notice the rpms drop. This is one (or more) of the cells in the pack running out of charge and the ones remaining will be reverse-charging it. Before too long you'll find your drill lasts nowhere near as long as it did when it was new.

Big Clive did a video about them on YouTube once, if I recall. I'll see if I can find it.

 

[iainfm]

I think this is the one I'm thinking of, from the 3 minute mark or so:

 

[marcopolomt]

You say you are not a novice in the EV ownership stakes, and then criticise MG for not being able to limit a charge to 80%. Did you not do the appropriate research first? If not, the fail is with you. And apologies for being so blunt, but I am a complete novice with EVs, but I did know this limitation before I bought the car. It was pretty easy to find out.

I am a current leaf owner but there is a workaround with the leaf through the charge timer. a bit of maths and i worked out not to bother charging until the battery drops below 50% on my granny cable. I never considered an mg ev up until the announcement of the 2022 ZS EV due to the omission of charge limiters/timers.

I’m not sure any manufacturer recommends only charging to 80% - this arbitrary figure seems to be based on the point where, roughly, charge speed begins to slow. I guess now one wants to include the slower charging percentage and make speeds look bad!

It’s mentioned several times in the owner manual when talking about time to charge from the point where low charge warning appears (20%) to this 80% value.

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from my knowledge of lithium-ion cells dendrites build up with more extreme battery temperatures and also charging to high capacity. Sure, the battery may be guaranteed for 8 yrs, but you don't want a battery with just 75% capacity after 8 yrs. Remaining capacity will be as important on the used car market as age and mileage over time. Don't over-think it but if you can keep batteries between 20 and 80% you can sustain your battery capacity for longer.

Thankfully it appears MG are introducing charge limits AND a timer with the new ZS. Those features aren't on any stelantis vehicles which are usually dearer than the ZS (they only have start charge timer). These features are much overlooked with EV car buyers but are important in the long term.

 

[marcopolomt]

I might be missing something, but doesn't the BMS take care of this already? The % indicated on the dash to the driver is not the full battery capacity, it's the percentage of the usable capacity...which is around 93% of the total capacity according to EV database. (Almost identical for LR and SR).

Yes, this is higher than 80% but I'd like to think that the manufacturers (of the car, battery and battery management system) have made sure this is the optimal balance of range and battery durability.

indeed, most manufacturers limit the useable capacity to prevent the worst problems but even with a smart phone you will find it lasts a lot longer if you keep the battery charge between 20 and 80%.

 

[Petriix]

There's a highly illogical tendency for people to believe that, because the BMS prevents use of the extreme ends of the battery voltage, this somehow eliminates all degradation. That's obviously nonsense.

Battery degradation is a curve. The closer it is to 'full' or 'empty' the more the battery will degrade. If the BMS didn't protect it then it would rapidly lose capacity, but that doesn't mean that it will miraculously retain its original capacity forever.

 

[smokie]

Doesn't it manage itself to some degree by using cells from the pool though, swapping bad for good as it ages?

 

[Petriix]

Doesn't it manage itself to some degree by using cells from the pool though, swapping bad for good as it ages?

No, you seem to have a fundamental misunderstanding about how EV batteries are wired. It would be highly wasteful to carry around redundant battery cells; why wouldn't you just use them all from the start (hint, this is what they actually do) and have a higher overall capacity and put less stress on each individual cell?

The idea is that all the cells are used as evenly as possible and kept as close as possible to the same voltage (as each other). When some cells have a lower voltage than others, the overall usable capacity of the entire module is reduced. This is because, to avoid over-discharging the lowest cell, no further discharge is possible once that single cell's voltage reaches the lower safe limit (even if there is lots of energy stored in the other cells, it can't be safely accessed); and, to avoid overcharging the highest cell, charging must stop* as soon as that single cell reaches the maximum safe voltage (even if there is plenty of capacity left unused in the other cells).

*There is a balancing process at the end of charging where the highest cells are protected by switched resistors to allow other cells to be brought up to the same voltage. This is a slow and lossy process so it's better to avoid letting the cells get too far out of balance.

 

[smokie]

Despite your rather patronising tone at the start of your post you seem to not realise that some car batteries do retain a pool of unused cells.

You may not agree with their logic but it's a fact that they do.

See Chevrolet Volt - Wikipedia where it says "For the 2011/2012 model years, the battery pack stores 16 kWh of energy but it is controlled or buffered via the energy management system to use only 10.3 kWh of this capacity to maximize the life of the pack."

I don't believe that is the only car to operate that way.

 

[Petriix]

Despite your rather patronising tone at the start of your post you seem to not realise that some car batteries do retain a pool of unused cells.

You may not agree with their logic but it's a fact that they do.

See Chevrolet Volt - Wikipedia where it says "For the 2011/2012 model years, the battery pack stores 16 kWh of energy but it is controlled or buffered via the energy management system to use only 10.3 kWh of this capacity to maximize the life of the pack."

I don't believe that is the only car to operate that way.

Like I said, that's not how it works (apologies for appearing patronising though). The capacity is limited by restricting the voltage range within which the cells operate, not by retaining 'a pool of unused cells'; that's a rather bizarre assumption on your part. The nominal capacity of the cells assumes that they will operate across their entire safe voltage range whereas the 'usable' capacity refers to the bit that the BMS actually utilises.

The advantage of doing this is that the battery will appear to never lose any capacity (all the degradation will be within the hidden buffers) and it can be charged a full speed all the way up to 'full' without causing much damage. The Volt is a rather extreme example of this, but all EVs limit the battery capacity to some extent.

 

[smokie]

On reflection, I realise that I may have interpreted the Ampera stuff wrongly (over many years I might add!!), by assuming it was working in a similar way to the "bad block pool " on a hard disk drive, whereby bad blocks are marked as unusable and replaced with one from the pool (until it is exhausted). I think your term "hidden buffers" is what I assumed were unused cells.

But you are effectively saying that the battery capacity is somewhat more than the usable capacity, and it is managed by the BMS, aren't you?

If so that is effectively redundancy by design, just not in the way I visualised it. As in you could use a greater percentage of each cell to achieve the same storage with less cells (but for practical reasons they don't).

Whatever, so long as it works

 

[Petriix]

On reflection, I realise that I may have interpreted the Ampera stuff wrongly (over many years I might add!!), by assuming it was working in a similar way to the "bad block pool " on a hard disk drive, whereby bad blocks are marked as unusable and replaced with one from the pool (until it is exhausted). I think your term "hidden buffers" is what I assumed were unused cells.

But you are effectively saying that the battery capacity is somewhat more than the usable capacity, and it is managed by the BMS, aren't you?

If so that is effectively redundancy by design, just not in the way I visualised it. As in you could use a greater percentage of each cell to achieve the same storage with less cells (but for practical reasons they don't).

Whatever, so long as it works

Yes, but the difference is that the cells suffer less degradation when used within the middle of the voltage range. Fewer cells with a smaller buffer would suffer greater cumulative degradation.

 

[VinnieP]

Is there any real world evidence that charging to 100% each day has X amount of negative effect on the battery?

I ask as I will be charging to 100% each day because I don't know where I may be needed in my job, could be 40 miles or 200. Not got my vehicle yet unfortunately to comment on this in real world terms.

Yes, I think there is enough evidence to confirm this.
The most recent study of this I can find is from 2020, saying it is detrimental to battery life to go below 20% or above 80%.

Source here

 

[SDP79]

You say you are not a novice in the EV ownership stakes, and then criticise MG for not being able to limit a charge to 80%. Did you not do the appropriate research first? If not, the fail is with you. And apologies for being so blunt, but I am a complete novice with EVs, but I did know this limitation before I bought the car. It was pretty easy to find out.

Sorry for not being knowledgeable about every aspect of the car. Clearly not as clever as you. If everyone knew all there was to know about the car then forums like this would not be needed. I raised an issue that I thought would be of interest to many. Having looked at the MG handbook again I can see that there is no direct reference to charging to only 80% or indeed any specific way of limiting any charge other than by monitoring yourself and unplugging when appropriate. I had done research but silly me I did not have all aspects of the car to hand. Some of the issues raised on the forum were ones that I knew about, but I resisted the temptation to belittle those that raised them. I have owned a NIssan Leaf EV for nearly 2 years before buying this MG5. These are not bragging rights just facts. I learnt much more about the car after purchasing it, even though I had done research before purchase. I still did not know everything about the car. I am now in a similar position with the MG. I am learning and will continue to do so throughout my ownership. I shall have to give very careful consideration before asking any questions on this forum again.

 

[weedavemac]

Sorry for not being knowledgeable about every aspect of the car. Clearly not as clever as you. If everyone knew all there was to know about the car then forums like this would not be needed. I raised an issue that I thought would be of interest to many. Having looked at the MG handbook again I can see that there is no direct reference to charging to only 8% or indeed any specific way of limiting any charge other than by monitoring yourself and unplugging when appropriate. I had done research but silly me I did not have all aspects of the car to hand. Some of the issues raised on the forum were ones that I knew about, but I resisted the temptation to belittle those that raised them. I have owned a NIssan Leaf EV for nearly 2 years before buying this MG5. These are not bragging rights just facts. I learnt much more about the car after purchasing it, even though I had done research before purchase. I still did not know everything about the car. I am now in a similar position with the MG. I am learning and will continue to do so throughout my ownership. I shall have to give very careful consideration before asking any questions on this forum again.

Excellent.

 

[Prof1967]

I think the whole charging to 80% really depends on how long you intend to keep the car.

Saw a video to day where someone has a 2014 Tesla with 125000 miles on the clock and in that time battery efficiency has dropped by 8 per cent. Also mentions that the battery takes slightly longer to charge.

The owner says he is hoping to keep the car going for at least another 125000 miles.

 

[marcopolomt]

I think the whole charging to 80% really depends on how long you intend to keep the car.

Saw a video to day where someone has a 2014 Tesla with 125000 miles on the clock and in that time battery efficiency has dropped by 8 per cent. Also mentions that the battery takes slightly longer to charge.

The owner says he is hoping to keep the car going for at least another 125000 miles.

I'm assuming this was James Cooke?

teslas encourage you to only charge to 80% for day-to-day driving and only to the max for road trips. they have also been leaders in battery management for donkeys. my 2018 leaf has 40k miles on the clock and 90% battery capacity. there's the difference.

If I were buying a used EV I would want to check the battery capacity before buying (already is with the leaf and leafspy). it will be more common in the future so it makes sense not to abuse the battery too much.

 

[EVsince2016]

Despite your rather patronising tone at the start of your post you seem to not realise that some car batteries do retain a pool of unused cells.

You may not agree with their logic but it's a fact that they do.

See Chevrolet Volt - Wikipedia where it says "For the 2011/2012 model years, the battery pack stores 16 kWh of energy but it is controlled or buffered via the energy management system to use only 10.3 kWh of this capacity to maximize the life of the pack."

I don't believe that is the only car to operate that way.

It still uses ALL of the batteries it just doesn't fully charge or empty their capacity

The warranties allow for charging to 100% & running them flat, but then you could be left with a battery with 75% capacity within the warranty. Keeping them 20-80% minimises the capacity loss. Yes few manufacturers state this, some rapid chargers set this limit but it does not affect them adversely.

Whilst today selling an EV no questions are asked, in the futures buyers will expect to do a battery health check and your cars resale value will be based on that.

There is a lot to learn with EVs even if you have owned one for a few years. I am at 5 years and there is still so much to learn not in least because things are changing fast still.