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In order to try to increase my knowledge of all things EV related (which is not difficult) I have subscribed to the weekly emails that Motability provide over 6 weeks. This weeks email is about charging costs. I was surprised to read that average cost per mile if you rely on fast chargers or rapid chargers is more than running a petrol car but, that aside, I am confused by the equation that they show to calculate how much it would cost to charge an EV. They state that to work out how much it will cost to charge your car you perform the following calculation;
My home electricity costs 26.85 pence per kWh. If I take the BMW iX1 as an example, it has a 150kwh battery. So that is 26.85p x 150 (=£40.27) divided by 100 equals 40.27 pence to fully charge the vehicle. Clearly nonsense, so what am I doing wrong?
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In order to try to increase my knowledge of all things EV related (which is not difficult) I have subscribed to the weekly emails that Motability provide over 6 weeks. This weeks email is about charging costs. I was surprised to read that average cost per mile if you rely on fast chargers or rapid chargers is more than running a petrol car but, that aside, I am confused by the equation that they show to calculate how much it would cost to charge an EV. They state that to work out how much it will cost to charge your car you perform the following calculation;
My home electricity costs 26.85 pence per kWh. If I take the BMW iX1 as an example, it has a 150kwh battery. So that is 26.85p x 150 (=£40.27) divided by 100 equals 40.27 pence to fully charge the vehicle. Clearly nonsense, so what am I doing wrong?The battery usable capacity is 64.7 kWh. 150 is the power of the iX1 30
26.85 x. 64.7 divide by 100 = £17.37
Hope that helps
Thanks @Debs I realise now that I was being ultra thick and when working out 26.85p x 150 I was converting that into pounds before dividing by 100, whereas the divide by 100 does that – so I was doing it twice. It’s been a long day ?
Plus I thought that the 65 kWh was the charging speed, not the battery capacity. As I say, I’m starting from a very low base ?
@Glos Guy – two things:
1). The battery capacity of the iX1 is not 150kwh. That is the maximum rate at which it can charge on a rapid charger. The capacity is probably around 60kwh for the 20e (I’d have to look it up to give an accurate figure). The i4 e35 I have on order has a battery capacity of 71kwh (actually 67kw usable), so using your electricity price the cost for a full charge would be £17.99.
2). However, the idea of a home charger is to take advantage of the smart charging rates available, the best of which is currently Intelligent Octopus Go, which provides a guaranteed 6 hours at 7.5p per kwh, plus random cheap hours during the day based on when Octopus decide the grid is underused or that there is a surplus of power. These charging schedules are sent to you via an app.
In addition, whenever the car is plugged in and charging on the smart tariff, the whole house (washing machine, dishwasher etc) is also charged at 7.5p per kw.
So the i4 would cost just over £5 for a full charge and around 265 real world summer miles. Not bad huh? ?. Deduct 20% or more for cold winter days.
In reality, the costs are a little higher due to small losses during charging.
Believe me, I was where you are before looking at the i4 and have spent months researching the subject!
What is needed perhaps is a different mindset to how many miles you add overnight. Don’t need the full 265 miles by morning? Fine, just add 60% or whatever. Not planning a long journey tomorrow? Fine – Don’t plug it in for a few days.
After all we don’t usually top up with petrol every time we return home in a ICE car.
Your X1 has been considerably more parsimonious than our XC40. While it can manage 45mpg on a good run, the reality is that many short journeys have brought down the average to 33.2 over the 3.5 years we’ve had it, so I’m very confident that with a predicted charge-at-home ratio of 90:10, our running costs are going to be hugely reduced, even allowing for a big jump in electricity prices and occasional rapid charge when on holiday/visiting family etc.
Caveat: we only cover around 6000 miles annually and much of these are local miles. If you are a high mileage user, or are unable to charge at home on a smart tariff for the majority of the time, the an EV, at this current time, is probably not for you.
Hope this puts a more positive slant on it!
2024 - BMW i4 Grand Coupe eDrive 35 Sport
2020 - Volvo XC40 T4 Inscription
2017 - Audi Q3 TFSi Sport S-TronicI see Motability’s assumption is based on easy maths 0-100%, when in reality you mostly charge from 20-80% and thus need to know what 60% of a given battery size, to work out the cost to charge.
The iC1 has a 64.7kW useable battery – 60% of 64.7 = 38.82kW’s needed to charge from 20-80%
Price per kWh x (60 x 64.7 / 100) /100
Why stop at 80%? Just charge it to 100% at home. Get a full tank out of it?
Well yeh, why not but, you still got to wotk out the percentage of the battery your actually charging, as you’ll highly unlikely to be charging from 0%.
Doesn’t 80-100% take a lot longer? Pretty sure charging a battery isn’t as linear as that calculation would have you believe.
@kerzo
I know, but ev,s are the same as ice cars. I would fill the ice tank to full and similarly the ev.
Only difference is the ev is more accurate how many miles you got left.
Nearing handover of the petrol car, i was only putting a tenner in it. Not much point in handing over the car with a full tank. But the car said 188 miles left, an drove 20 miles home an it still said 188 miles. Next day on startup its down to 160 miles.
Not bothered about miles or range, with ev or ice. When it got to half tank it got filled up.
I.ve not found any problems getting a place to charge the ev.
The only problem is getting one that is affordable.
The cheap rate rapid chargers at 17p kw/hr are busy. The 70p/ kw.hr 150kw sit empty, 6 charging bays, an at most only seen one car using it
But next to a starbucks, plug it in go for a coffee an its charged by the time am half way through the coffee.
Am gonna need new clothes at this rate.
I see Motability’s assumption is based on easy maths 0-100%, when in reality you mostly charge from 20-80% and thus need to know what 60% of a given battery size, to work out the cost to charge. The iC1 has a 64.7kW useable battery – 60% of 64.7 = 38.82kW’s needed to charge from 20-80% Price per kWh x (60 x 64.7 / 100) /100
How do you find out what the ‘useable battery’ size is? Is that the second number in an EVs model description, because I thought that was the charge rate? I know that most people on this forum are EV enthusiasts and get all of this, but for those of us who don’t it’s so ruddy confusing and I’m not surprised that EV take up amongst private buyers is so low. I currently have a 2.0 litre petrol that does around 43mpg and has a range of around 600 miles. My brain can cope with that. I think I shall need to take an Open University degree to understand what all the EV numbers mean in the real world.
Given that EV range isn’t great to start with and drops far quicker than an ICE car in colder weather or if not driven fairly sedately, I think I would always charge to 100%. I accept that it would never be zero to start with though (well hopefully not ?)
Thats what i.m trying to say Glos.
If you look at it as tank size, or percent full, then its not a problem for most part. The only time you have to plan anything if you are on a long trip in an ev. Then you have to put a smidgen more thought into it.
With a mobility car, you are covered by the rac. If your car runs out of petrol or charge, they come out an fix it.
I see Motability’s assumption is based on easy maths 0-100%, when in reality you mostly charge from 20-80% and thus need to know what 60% of a given battery size, to work out the cost to charge. The iC1 has a 64.7kW useable battery – 60% of 64.7 = 38.82kW’s needed to charge from 20-80% Price per kWh x (60 x 64.7 / 100) /100
How do you find out what the ‘useable battery’ size is? Is that the second number in an EVs model description, because I thought that was the charge rate? I know that most people on this forum are EV enthusiasts and get all of this, but for those of us who don’t it’s so ruddy confusing and I’m not surprised that EV take up amongst private buyers is so low. I currently have a 2.0 litre petrol that does around 43mpg and has a range of around 600 miles. My brain can cope with that. I think I shall need to take an Open University degree to understand what all the EV numbers mean in the real world. Given that EV range isn’t great to start with and drops far quicker than an ICE car in colder weather or if not driven fairly sedately, I think I would always charge to 100%. I accept that it would never be zero to start with though (well hopefully not ?)
You don’t want to be charging your EV to 100% at a public charger the EVangelists would chew you a new one lol – the wait is real 😛
You don’t want to be charging your EV to 100% at a public charger the EVangelists would chew you a new one lol – the wait is real ?
? Thankfully, if I get an EV, I will be charging at home, other than when we go on longer trips. I’m aware that the 80-100% charging takes an eternity, so it’s not worth doing that on longer trips (which is a pain, as it further reduces the real world range at the time that you most need it) but is the 80-100% charge proportionately more expensive (as it takes longer) or does it cost the same as the quicker 60-80%?
Hi
We have the e2008 and had it just under a year now, done about 5000 miles in it,
right, we often will charge up to 100% but dont need to normally, just like a ‘full tank’ in the summer we got nearly 200mile before i started to worry, 99% of the time we are withing 10mile (if not a lot less) from home.
we do say 100miles a week so i charge on a Saturday night to top things up, we are on Qctopus and get a 7.5p/KW rate from 11:20 to 5:30am each night, we put the washing machine and dishwasher etc on timer so we find that with us using the dishwasher/washing machine/dryer etc each night (need to for or disabled sons problems) we are in fact spending less in electric now than before we had the car and that incudes the cost of charging the car, we are also saving all the cost of petrol (about £100 per month) so for us its a no brainer.
one or twice a year we venture further way from home and have had to use public chargers twice i think and yes they are not cheap but neither is motorway petrol and i dont think we spend more than if we used a ICE car for that run anyway.
the normal thing to do at public chargers is to charge up to 80%, the reason being the high charge rates that are needed to pump all the electricity into the cars batteries can shorten the life of the battery pack due to heat etc as the cells get full so cars automatically slow the charge rate once you get to 80%, it takes a long while to go from 80 to 100%, that ties up the charger for other users, up to 80% can normally be done in 20-30mins for most cars (not normally at zero when you start , unless you push the car there!)
if you do stay longer (no one waiting and your still drinking your coffee etc) as the charge rate drops you will find your the cost per hr drops, your billed for the electric you use , not the time so although it takes a lot longer to go from 80-100 % the cost for that last 20% would be the same as the first 20%.
i will admit i always worry about if the public charger will work, be available etc but thats only because its so rare i use one, i think its been maybe 3 times in the last year certainly not more and havent had a problem at any time. we are very happy driving a EV and will certainly go down that route again, dont forget that you get a free home charger too (worth about £1000 fitted) ifyuo can have a home charger, dont do much more than 100miles a day its got to be the way to go IMHO.
As regards charging to 100% at home, well its not such a strain on the battery pack as the charge rate is a lot lower on a home charger so it doesn’t heat the battery pack the same as a rapid charger would and also , to be honest 99% of EV’s have a buffer that stops the battery from reaching a real 100%, for example our car as about 50KW battery pack but full charge is stopped at about 45KW to protect the battery, all that is automatically managed by the cars systems so you don’t have to think about it, just plug in and let it get on with it.
I know EV dont suit everyone, if you cant charge at home, do high mileage each day but for us we love it.
If you’re doing ‘normal’ mileage through the day then it matters not one jot whether you charge to 80%, 90% or full, what matters is how much you use and when you intend to put it back.
Let’s say, purely for argument’s sake, that your car can do 250 miles per charge and you work 25 miles from home. In a petrol car you’d top up once all the way up to full and then run it all the way down to something near 10-20% then you’d top up again. That’s economy of effort, you have to go to a petrol station to top up.
In an EV it’s all about time. If you get 6 hours of really cheap charging time, and your car takes 9 hours to fully charge, you don’t want to get to empty, it costs more to get back up to full. Likewise, if you park in your drive every day, what’s the additional effort to get the car charging? You have to put the cable in the sockets, one in the charger (unless it’s already there) and then in the car. Timers are usually set, either in car or on the charger to make the most of the cheap rate, so it’ll put power in for whatever time you want and you can even set car or charger to stop at a certain percentage full, so you can just go up to 80% if that’s your thing.
Getting back to the example, you use 20% of the capacity to get to and from work, you could charge weekly if that’s all you do but Friday’s home trip could be a little exciting. You could charge it up on Sunday, then again Monday evening, Wednesday Evening and Friday evening for the weekend. That way, there’s no chance of running low for unexpected journeys and you’ll never experience range anxiety in normal use. You make the most of charging only in these cheap times and, if you’re off somewhere for the weekend, you can charge to 100% on that Friday night, get up Saturday morning and off you go in a full car.
Even driving long distances you don’t need to feel range anxiety. The car does 250 miles, that’s 4 hours at 60mph and 3.5 hours at 70. By the time I’ve driven 2 hours I’m desperate to get out of the car and walk somewhere. So, instead of parking in a disabled bay and wondering around, park in a charging bay, plug in and go for your wonder. By the time you’ve been to the loo, got a coffee and got back to the car, you’ll be ready for more than the next 2 hours.
There’s a saying in the EV world – Don’t stop to charge, charge when you stop. It’s as simple as that, whenever you stop on a long journey, plug the car in, as long as you’ve driven more than 10 miles, the car will probably benefit from that charging time and, if there’s no chargers available the world hasn’t ended.
I'm Autistic, if I say something you find offensive, please let me know, I can guarantee it was unintentional.
I'll try to give my honest opinion but am always open to learning.Mark
Thanks @Paul_1964 That’s very useful. By my quick ‘back of a fag packet’ calculations, if you were spending £100 a month on petrol whilst only doing 5,000 miles a year, your last car only did around 25 mpg. I’m not surprised that you switched to an EV! Thankfully, my current petrol car achieves around 42 mpg.
Running costs aren’t terribly high on my priority list when it comes to choice of car, so I’m happy to pay more to drive around in a car that gives me pleasure and only requires a 5 minute petrol stop once every 2-3 weeks, but with Motability now focussing so heavily on EVs, especially at the upper end of the scheme, if we stay with Motability I’m going to have to seriously consider one.
Thanks for explaining the 80-100% issue. My only worry with that is that if only charging to 80% the already low range is reduced even further. I accept that petrol is mind blowingly expensive at motorway service stations, but as my petrol car has a range of 600 miles I never have cause to use them. Possibly they are less easy to avoid with an EV though on a long journey? All interesting food for thought though, especially as we can charge at home and most of our journeys are well within the range of EVs, even in the winter when the range drops. It’s the longer journeys that trouble me. On a long journey we only make very short stops for the loo. We don’t have coffee breaks, so the need for a 20-30 minute stop would be a pain.
Charging the battery to 100% regularly can accelerate battery degradeation over time. Charging via a rapid charger at a motorway services from time to time or even letting it charge to 100% if time allows on them odd longer journy’s, isn’t going to cause much in the way of harm.
All EV’s have a safety buffer, The e2008 for example has50kWh battery but only 46.3kkWh is useable. A similar buffer will also be at 0%. The e2008 is also capable at charging upto 100kW. Plugging into a motorway services 150kw, your car will throttle the charge and the likely hood your paying over the odds using a 150kW or higher charger.
Like @Glos Guy we only stop for a quick pee and were back on the road again to our destination. If I’m travelling alone to my parents three and half hours away, I’ll do my dam best not to stop at all.
Charging the battery to 100% regularly can accelerate battery degradeation over time. Charging via a rapid charger at a motorway services from time to time or even letting it charge to 100% if time allows on them odd longer journy’s, isn’t going to cause much in the way of harm. All EV’s have a safety buffer, The e2008 for example has50kWh battery but only 46.3kkWh is useable. A similar buffer will also be at 0%. The e2008 is also capable at charging upto 100kW. Plugging into a motorway services 150kw, your car will throttle the charge and the likely hood your paying over the odds using a 150kW or higher charger. Like @Glos Guy we only stop for a quick pee and were back on the road again to our destination. If I’m travelling alone to my parents three and half hours away, I’ll do my dam best not to stop at all.
The other thing that needs to be taken into consideration is that manufacturers state that a battery shouldn’t be regularly charged above 80% or let fall below 20% if you want to keep it in optimal condition. Therefore if you follow these guidelines for the majority of the time you use your EV you should only ever use 60% of your cars range for the majority of your driving needs.
Like with any other type of car quoted ranges rarely turn out to be achievable most of the time so if you are one of those people who follow the instructions to the letter to prolong car life you are only ever going to get just over half of your cars quoted range at best between charge cycles
This weird belief by everyone, including manufacturers, that a battery shouldnt be charged to 100% is surely a strange one. we’ve all been driving cars with 12v batteries for quite a long time, but we’ve never been told to keep it at 9.6v for battery health, and they regularly charge at an estimated 14.4v. Have a read of this article, they do some good research into EV cultures, myths and facts
Alsoi in regards to running costs that have been mentioned a few times, Which! done a fairly comprehensive study earlier this year which is quite a good comparison tool between ICE and EV, it’s quite unbiased and presents a fair picture on price parity and the like
The other thing that needs to be taken into consideration is that manufacturers state that a battery shouldn’t be regularly charged above 80% or let fall below 20% if you want to keep it in optimal condition. Therefore if you follow these guidelines for the majority of the time you use your EV you should only ever use 60% of your cars range for the majority of your driving needs.
Letting the battery drop below 20% or even below 10% is rarely cause for concern. Permanently low states of charge below 20% for long periods of time will carry the risk of total discharge. Continuous restarting a fully discharged lithim battery, will not only affect its longetivity but also the amount of charge the battery will hold. Unlike older battery technologies, lithium batteries don’t suffer from memory effect however as more sustainable battery technologies are in the works for EV’s, they may wel be affected by the memory effect.
This weird belief by everyone, including manufacturers, that a battery shouldnt be charged to 100% is surely a strange one. we’ve all been driving cars with 12v batteries for quite a long time, but we’ve never been told to keep it at 9.6v for battery health, and they regularly charge at an estimated 14.4v. Have a read of this article, they do some good research into EV cultures, myths and facts
I question much of the logic in the link provided.
Each cell in a 12v lead acid battery should be 2.2V nominal and have no less than 12,6V when the enhine is not running. Withe the engine running, the alternators voltage regulator will keep the output between 13.5-14V with an optimal output of 13.8V, a float charge of 2.25 to 2.27/8 (can’t remener per cell. Any higher than that, the battery could be fried. A battery at 9.4V has 2 dead cells, even at 9.6V it wont hold its charge.
Charging lithium batteries like NMC and NCA to 100% continually will have a negative affect over time. The difference between the total capacity of the battery and the useable amount that can be drawn upon, is there so you don’t fully deplete every last bit of energy in the battery when driving, thereby damaging or shortening the life of the battery. The vehicle will come to a halt or go into limp mode long before this point is reached, this point is often below the guage showing 0%, hence the vehicle will travell a little further before it actually hits the buffer.
Letting the battery drop below 20% or even below 10% is rarely cause for concern. Permanently low states of charge below 20% for long periods of time, such as leaving the vehicle standing for weeks on end carries the risk of total discharge, Its easier for manufacturers state 20%, than waffle on in the small print nobdy reads,
Batteries like NMC NCA charged to 100% is actually 100%, frequently charging to 100% will negatively affect the battery longterm. Whils’t charging the useable battery capacity 20-80% or 0-80% you will only get 60 or 80% per charge cycle. Even charging 0-80% charge cycle will degrade the battery 5x less than charging to 100% – 5×80% – 400% compared to 1×100% =100%, if charging to 100% all the time. In laymans terms the battery will beable to be charged many more times and will last longer. Lithium batteries don’t degrade linear. The BMS slows the rate of charge at after 80% to prevent heat damaging the battery.
The i-miev had a range of 50 miles 80km’s, so getting 110km’s plus and 70km’s after 13yrs I personally find odd. Unless of course he isn’t telling us he had what was at the teme a common battery upgrade on his i-miev!!
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