The preserved wisdom from people who actually drive EV’s is that once a month it is good form to charge to 100% as the Battery Management Systems does lots of work in the final 10% from 90-100% charge, managing and balancing out the cells, that final 10% often takes longer than it takes to go from 20-80%.
Yes. That’s, as you mentioned, because EV chargers “balance charge” rather than just charge. Where you’re wrong is the “good to charge to 100% once per month” – there’s literally zero upside to it. It doesn’t do any good. I’ve worked with batteries for almost a decade now, i’m very certain of that. All this “preserved wisdom” is, is the equivalent of “boot her once per drive to clean the catalytic converter”.
It’s not how it works.
You also need to be aware that all batteries have buffers, so when the car shows 0% or 100% state of charge, the battery is actually nearer 5% and 95%, theses buffer zones are unusable to the car, but are there to protect from fully discharging and killing a battery.
That’s partially correct. While true that you have buffer zones (plus overcharge and over-discharge protection, obviously), the voltage remains the same. It’s 3.7V nominal, or 4.2V on full charge – even if it’s only at 95% capacity. And that’s where the problem is.
AC (Slow) charging is believed to be healthier for batteries, but there are plenty of people (me included) who do that vast majority of charging via DC fast chargers, and are seeing no degradation of batteries (Taxis with well over 120k miles all on DC and battery still healthy). Currently I’m getting around 340 miles on a 100% charge.
No, it’s a fact. As in, physical fact. The more you strain the battery, the more it degrades. What’s happening is that, under load (particularly, when hot), the electrolyte in the batteries split (it’s called electrolytic decomposition, and well known. It’s also visible to the naked eye, but because packs are usually not visible in an electric car, that indicator falls away. What’s happening is, that under load and high voltage, the “stuff” in the batteries decomposes, into lithium and oxygen (amongst other stuff, but those two are the important ones) – which leads to two things. A: the batteries visibly grow in size (they “puff” due to the internally released gas), and B: the internal diodes of the battery corrode (that’s the battery degradation, plus of course the loss of carrier-electrolyte).
The biggest thing personally to understand is how you car behaves to charging, and the benefits of different types of charging. I don’t think many new EV owners (Or dealerships) understand how the cars work. Take the Kona for instance, it has a 64kW (Usable) battery, and will charge at 11kw on AC and 77kW on DC, sounds great… But it will only charge at 77kW for a very short time and only at a specific battery state and temperature, if it’s not in the sweet spot, it will be much slower. The same goes for chargers, you are lucky to get much more that 44kW from a 50kW charger.
I actually do agree that dealerships don’t seem to understand how EVs work, but it’s hard to blame them. I’ve worked with various variations of lithium packs in the last decade (Li-Ion, Li-Po, LiFe-Po4), and it’s not like your average AA battery – nothing with them is.
The very fact is, to prolong the life of a battery (any lithium battery), you only charge it to slightly above their nominal voltage (3.7V), and discharge it slightly below. That’s where these batteries are “storage charged” as well (i don’t think EVs have that option, though imho they very much should – but that’s how they’re charged by the factory – to roughly 40% capacity and 3.7V, because that’s where the least degradation happens). Everything above 3.7V is various levels of bad for the battery, getting worse the higher you go. That’s why “charging to 100% (regardless of whether it actually is 100%, or 95%) isn’t good for the battery and should only be done if you need the range.
One should also mention that while i agree that dealerships/salesmen are clueless, those battery warnings don’t come from the car manufacturer, but the battery manufacturer, just relayed.
Lastly: batteries have come a long way in the last decade or two, and the degradation is nowhere near what it was even 5 years ago (if i recall the article correctly, it’s almost slashed in half) – but basic physics and chemistry don’t change. The packs are more resistant, but they still degrade. And they will always degrade for the same reasons, until we get to solid state batteries (not another decade, would be my guess) that don’t require an electrolyte. This is all kinda moot though, since we only have the car for three to five years, even if you blast it, at most you’ll lose around 15% in that timeframe. Which, btw, doesn’t show in the indicator. The indicator doesn’t measure the internal resistance of the battery (which increases due to the poles corroding through released oxygen/lithium), which means that the battery indicator can read 100% (or 3xx miles), but the battery discharges itself completely within 100 miles (extreme example).
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.