296 The Battery Charging Percentage Episode

Gary Comerford (: 00:00

Hi, I'm Gary and this is EV Musings, a podcast about renewables, electric vehicles and things that are interesting to electric vehicle owners. On the show today, we'll be looking at how much you should charge your EV and when.

Last May, I took my iPhone to the local Apple store and they ran a diagnostic and told me that the battery in there was currently at 78 % state of health. And that meant that when the display told me it was at 100, it was actually only at 78 % of the full battery capacity.

As a result, my phone needed charging more often, didn't last as long to charge and was, not to put it too finely, a pain in the arse. Or, as to those listening across the pond, they replaced the battery with a brand new one and I went happily away. Actually, I didn't. There was a timing misunderstanding and got managers involved, etc. But that's not the point of this story. Ask me about it if you ever meet me in person and want the full down low on it. Now we're now 12 months later.

And I've just checked my iPhone and the battery is now at 91 % state of health. So it's already degrading. Now we've all got phones now. The universal thing about phones is that it doesn't matter how long you have them or how you charge them, sooner or later you'll look into the settings and you'll find your batteries at 80 % state of health or lower. I suppose that's why many people opt out for a new phone every year when in reality a new battery is all that's needed. So why is degradation so bad on phones?

Well, there are many reasons for that and we've gone through them in other episodes and primarily it's the fact that phones don't have complex battery management and heat management systems. But outside of that, there are other reasons why your phone battery degrades quickly. And most of it is to do with how and when you charge it.

Now we get to that confession part of the podcast. Admit it. How many of you plug your phone in at night on the bedside table and let it charge while you're asleep? I see you in the back looking slightly sheepish. Come on, admit it. Of course you do. It just makes sense, right? You're not using it overnight. So why not let it charge? Well, unfortunately, you're actually damaging your battery, especially if you're one of a number of people who leave the phone in the bed with you.

under the covers while charging. Pretty much every domestic battery powered appliance, phones, vapes, laptops, toothbrushes is powered by an NMC, Nickel Manganese Cobalt Battery. The enemy of NMC batteries is heat. They don't like to be too hot. They don't like to get too hot when they're charging. Sidebar, actually they don't mind heat when they're charging as long as it's dissipated immediately after charging is finished.

Battery electrochemist Dr. Ewan McTurk told us that when he came in a while back to talk batteries.

So plugging in, putting it under the covers and letting it charge all night is damaging your phone battery. Even leaving it on the bedside table overnight to charge is bad because your phone is charging to its maximum capacity and staying plugged in. If you've got a phone like mine, it takes about an hour, an hour a half to charge. So if it's left plugged in for seven or eight hours, that's not good. So where am I going with this?

There are lots of people who will listen to this and they'll think there's no way I'm getting electric car if the batteries degrade like they do in my phone. Well, obviously they're not going to degrade that quickly. And we've recently done an episode with Aviloo where they showed us just exactly what sort of degradation you can expect on your EVs battery. The TLDR on that is the battery is probably going to last longer than the car it's in. But most people will charge their EVs overnight as they're sleeping.

And you can see how the parallels with leaving the iPhone plugged in on the bedside table or even worse under the covers with you will cause people to think that EV batteries will have the same degradation problems.

But the other factor that plays into a battery life alongside heat is how much and how often you charge it. So today we're going to take a quick look at when you should and shouldn't charge your battery up to a high state of charge. And before we start, we need to make sure that we're talking about the same things and define our terms. When we talk about phone batteries, we're usually talking about NMC batteries. These are the lithium ion batteries.

which have, as I've said, nickel, manganese and cobalt in them. These are the typical batteries found in most consumer goods, your phone, your toothbrush, vapes, laptops, rechargeable drills, anything. So they're also used a lot in electric vehicles, but they're not the only battery chemistry that's used. And the other main chemistry is called lithium iron phosphate or LFP. There's no cobalt in these and very little magnesium. It's cheaper and easier battery to manufacture. As Ewan McTurk said on the show, it's basically some lithium rust.

and bit of fertilizer. So why does some cars have an NMC and others have LFP? Well, there are pros and cons to each chemistry. LFP is better for charge cycles. It handles heat better. It's less likely to combust if pierced and it's cheaper, but it doesn't have as high a power density, which means that it won't go as far for a given battery size. 80 kilowatt hours of NMC batteries will have a longer range than 80 kilowatt hours of LFP batteries, but it will cost more.

Many manufacturers have installed LFP batteries in their bottom of the range cars and this makes them cheaper but reduces their range. That's why cars such as the 60kWh Tesla Model 3 Standard Range rear-wheel Drive have an LFP battery but the more expensive and longer range Model 3 Performance with a 79kWh battery uses NMC. It's the same for the Volvo EX30 single motor which has a 49kWh LFP battery but the 65kWh dual motor has NMC batteries. If however you're driving around in a BYD chances are

you've got an LFP battery regardless of the cost of the car or the size of the battery. They've patented a battery design called BYD Blade, which is 100 % LFP. And I'm pretty much sure all BYD cars use this. So how do you tell which chemistry you actually have in your EV? It's all well and good me talking about how you need to treat different battery chemistries differently. But if you don't know how to find this information, I might as well be talking Greek.

apologies to anyone watching or listening who is Greek. Luckily, there's a really easy way to find out. You go to the EV database.org and search for your car. Click into the entry for that car, scroll down to the part label battery, and you'll see things like nominal capacity, that's the full size of the battery including the buffer at the top of bottom, the architecture, whether it's 400 or 800 volt architecture, and the cathode material. That's what you're looking for. If it says LFP, that's the better but less powerful chemistry.

If it says NMC, that's the original, more powerful chemistry.

This is important because each of these chemistries needs to be treated differently to get the best out of it and preserve battery state of health for longer. So what are the differences?

You'll have heard me say numerous times on this show to not charge your battery above 80 % state of charge unless you plan to take a long drive. The reason for this is that once you start to approach the maximum capacity for a battery, it has some adverse effects on the health. It's a little like filling a balloon up until it's ready to burst. It's fine in the short term, push it a little too far and well, you know what happens next.

This applies to NMC batteries only though. If your car is one that has the LFP batteries, this doesn't apply. You can quite happily charge them up to 100 % day in and day out with no adverse effects. In fact, there is a school of thought that says that you should probably keep your LFP battery at 90 % or higher as often as possible. But, and I want to make this quite clear, what I'm not saying is that you can't let LFP go below 90 % state of charge and you can't let NMC go over 80 % state of charge.

That's absolutely not what I'm saying. You can quite happily charge an NMC battery up to 100%. All you need to remember is that you should really only do this if you're not going to let the car stand at 100 % for a long time. The typical example is when you go on a long journey. I might go up to my parents for instance. I usually have the car at 80 % state of charge until the night before I leave, then charge it to 100 % overnight, set off the next morning. As the charge has only been 100 % for a short period of time.

no issue. If I'm stopping to charge en route, I'll generally only send it up to 80%, not because it's harmful to the battery, but because it's quicker to charge to 80 % move on and stop further on the road if you need more charge than it is to stay on a charger from 80 % to 100%. This applies regardless of the battery chemistry you're using. So what effect does degradation have on your battery?

At a basic level, you would imagine, it reduces the effective range of your vehicle. If your original WLTP range is 200 miles and your battery degrades by 5%, you're going to lose 10 miles from the maximum range. If it degrades by 20%, you're going to lose 40 miles from your range. In winter, the range loss is going to be higher because the cold weather will reduce the maximum range anyway. And we talked all about this in the cold weather episode number 292.

The impression that many non-EV drivers have about degradation is that it matches that of a phone and your battery will be dead within three years, often resulting in it being thrown into landfill apparently. And that gives rise to what I call Schroedinger's battery. It's both too expensive to replace, but cheap enough to throw into landfill.

Of course, neither of these things are actually accurate. There have been many studies done on battery degradation and almost without exception, it's nowhere near as bad as people imagine. In fact, if you cast your mind back to the episode we did towards the start of this season with Dr. Marcus Berger from Aviloo Battery Diagnostics, you remember that he showed a graphic of all the battery health results that they've got from the tests they've done over the years. Two things.

stood out to me from those graphics. First, the difference in degradation between full battery electric vehicles and plug-in hybrid vehicles, and second, the relatively low amount of degradation that occurs as vehicle mileage increases.

Yes, there are outliers. The graph showed a couple of relatively low mileage vehicles with high battery wear. This could be due to a multitude of reasons, but the most likely is a faulty cell in the pack. But it also showed lots of high mileage vehicles with relatively low degradation, proving again that the battery health is much better than the naysayers would have you believe. So looping back to the beginning of this discussion, what's the best way to minimize battery degradation? Reduce heat, reduce cycling

ssipated quickly. The new BYD: 1500

probably isn't going to be an issue, but 100 days of 100 degrees Fahrenheit in Phoenix, Arizona, may well be. Secondly, reduce cycling. Now this is more difficult. A cycle is when a battery is charged and discharged 100%. This doesn't mean it's charged to 100 % then discharged to 100%. It means that 100 % of the battery capacity has been put in and 100 % has been taken out. So if you charge to 100, run it down to 50, then charge it up to 100%. That's half a cycle. If you do that twice,

full cycle. The more cycles the battery goes through the more degradation will occur. Obviously the more you use the vehicle the more the battery will cycle. The more it cycles the more it degrades but not in isolation. A vehicle that's charged slowly and regularly in cool conditions rather than in heat can have a lower degradation than the same vehicle that's done the same mileage but has been rapidly charged often and lives in a high heat environment.

So it's complicated. I think it's worth saying at the moment that this is a minor issue in the big scheme of things. If you live in a really hot country and rapid charge your EV at high kilowatt values multiple times a day, then you might need to look at what that's doing to your battery degradation. But if you're not in that situation, and I suspect the vast majority of us are not in that situation, then you're probably not going to have as much of a problem with your battery, if you have any problem at all.

As we come to the end of this episode, I want to summarise the situation and differences between NMC and LFP batteries. When you get your new or second hand EV, it's often best if you know the battery chemistry. Try asking the salesman to see if they know. There's a good chance they don't. My experience asking that question has about a 10 % hit rate. If they do know it, great. If they don't, go to Plan B, as we mentioned earlier, hit the evdatabase.org, look up your maker model and see what that says.

about the battery chemistry. Make sure you get the right make and model and the right battery size. As mentioned earlier, often the smaller battery size in a vehicle range is LFP and the larger can be NMC. once you know what battery chemistry you've got, you're in a great position to be able to understand how much you can charge your car on a daily basis. If it's LFP, go ahead and charge that puppy up to 100 % every night. No issue there. It's NMC and set that figure to 80%.

a more modern car there'll be a setting in the vehicle somewhere to define the maximum state of charge. In older vehicles you might have to rely on working out the time of charge to click off automatically on overnight charging. In other words if you have a 50 kilowatt hour NMC battery that's at 10 % state of charge you're going to want to add 70 % or 35 kilowatt hours to get it up to 80%. With a charger that averages 7 kilowatts you'll need to charge it overnight for five hours. You can set this either in the vehicle, in the cars app if it has one or in the charger app.

Once you've done that, just ignore things and live your life. There are a couple of ancillary things that we need to note. Some cars have 800 volt architecture so they can take very high charge speeds. Some only have 400 volts. This makes no difference to the battery. Both NMC and LFP can deal with that the same. Now throughout this episode, I've referred to stated figures such as 80 % and 100%. These should be considered normal figures, but not hard and fast figures. If you want to charge your NMC battery,

70 % or 85 % feel free to do that especially on an occasional basis. Likewise if you want to leave your LFP battery at 90 % not 80 % not 100 % from time to time that's also fine just don't make a habit of doing that. The other thing to remember with the battery at 100 % regardless of whether it's NMC or LFPs if you're driving at 100 % state of charge you find the regen braking or one pedal driving doesn't work quite as well.

And that's because both of these feed energy back into the battery. And if the battery is full, there's no way for that energy to go.

So what are your thoughts on battery degradation? Does it worry you? Is the thought of battery dag in a secondhand EV putting you off buying one? If it is, you really shouldn't get yourself a battery health check as we just discussed in episode 285 and help put that worry to rest in your mind. Remember, secondhand EVs have much, much better state of health than many people thought they were going to have a few years ago. Our discussion with Marcus Berger from Aviloo proved that.

Now, if this has been useful to you, don't forget to like, comment and subscribe, please.

I hope you enjoyed listening to today's show.

Gary Comerford (: 15:21

If you have any thoughts, comments, criticisms or other general messages to pass on to me, I can be reached at info at evmusings.com and on the socials I'm on bluesky at evmusings.bsky.social. I'm also on Instagram at EV Musings where I post short videos and podcast extracts regularly. So why not follow me there?

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Gary Comerford (: 16:50

If you've reached this part of the podcast and are still listening, thank you. Why not let me know you've got to this point by messaging me at musingsv.be, skies.at social with the words slow and steady hashtag if you know you know nothing else. Thanks as always to my co-founder Simone. He's an expert battery charger. Thanks for listening. Bye bye now.