Charging to 80%, does it really matter?

[james_scott22]

I know we are told to only charge to 80% to preserve the battery, and the car has a prompt recommending this. But assuming I'll only own the car for a couple more years on my lease, do we believe it really makes a difference? Charging to 90% would mean I could get two commutes out of my car between charges!

[Goaty]

I know we are told to only charge to 80% to preserve the battery, and the car has a prompt recommending this. But assuming I'll only own the car for a couple more years on my lease, do we believe it really makes a difference? Charging to 90% would mean I could get two commutes out of my car between charges!

Are you generally home-charging at no more than 7kWh? I’m not an expert and might quite possibly be corrected by someone, but I think it might be fast charging above 80% which could cause more issues than ‘trickling’ at 7kWh.
Plus I think sitting on a 100% charged battery for a few days is worse, than using it almost straight away after charging (on a regular commute for example).

I think your question will get some good opinions

[RichR]

The main detrimental effects on lithium battery life are caused by leaving it at a high state of charge for an extended length of time. However if you charge at home to 100% overnight and then drive somewhere at 8am, then it isn't going to be at a high state of charge for very long, so not really a problem.

There is of course a bit of a buffer at the top and bottom (ie 0% on the dashboard isn't really 0% in the battery, and 100% on the dashboard isn't 100% in the battery) - to allow for degradation over the years. ie an Enyaq 80 has a nominal 76kWh of useable battery, but the battery is actually more like 82kWh. All EV manufacturers do this now, so that a car sold as having 76kWh now, still has 76kWh for its whole expected lifetime (unless it's seriously abused). That wasn't always the case, and on smaller battery sizes (eg PHEVs with 7kWh batteries) degradation was noticeable after a few years. However this buffer isn't designed to be used to mitigate the effects of high levels of charge, and the BMU may well discharge it a bit automatically if left for a while (which is what things like laptop, mobile phone and drone batteries do) to extend the battery life and reduce the risk of battery packs swelling.

Charging at higher rates (eg DC rapid charging) causes damage in a different way, but the BMU does a pretty good job of slowing down the rate of charge and using the cooling system to minimise it. Again - EVs from 10 years ago suffered if they were mainly rapid charged, but that's not the case so much now as the management systems are much better at looking after the battery. Slow charging is always kinder, but again if you were to rapid charge to 90% at a motorway service station, and then get back on the road it won't be a big deal either.

So feel free to charge to 90% or even 100%, as long as you start using it within a few hours it won't do any real harm.

[Aragorn]

FWIW, i wouldnt say for sure the car will remain at 76kwh due to the buffer. The buffer shrinks along with the usable capacity. So for instance you i you started with 82kwh and 78 usable, and the battery degraded by 10%, it would now only have ~70kwh usable and ~73kwh total.

Even crappy batteries like my old LEAF 30 had a buffer, it was 30kwh nominal and 28kwh usable when new. After 80k miles it was down to about 24kwh usable. The LEAF batterys dont last as well as the newer tech though, so i would expect less degredation on my Enyaq at 80k miles. However i wouldnt expect none.

Deg is expected and normal in the 5-10% range even for the latest models at that sort of mileage, and its exacerbated by using the extremes of battery SOC. Doing it once or twice for a long trip ofcourse wont matter much, but pushing it to 100% every night certainly will.

Personally, in winter i charge to 90% as with a 60 it gives me a little more leeway for my commute. However given the choice of charging to 90 and trying to squeeze out two round trips or charging to 80 and only getting one, i would chose 80, because it keeps the battery away from the extremes. If you need that extra 10% to do two commutes, its likely you'll be pulling the battery down to a very low SOC to achieve it. The battery will much prefer being run from 80 to 40 twice, than it will from 90 to 10 once.

[Skeniv]

Just a week or so shy of 8 months with my Enyaq, I charge primarily overnight at home, always set to charge to 100%. Until the car goes in for its full service and they tell me otherwise regarding battery degradation I’ll continue to charge to 100% at home on my 7kWh wall box and up to the recommended 80% on public DC rapid chargers, which up until now I haven’t had a dire need to use regularly.

[HarryHuk]

80% is plenty for 3-4 days of commuting for me, and I can charge overnight.
I don't charge to 100% unless I'm going on a road trip, and I want to avoid/minimise public charging which is more expensive.

[Aragorn]

Just a week or so shy of 8 months with my Enyaq, I charge primarily overnight at home, always set to charge to 100%. Until the car goes in for its full service and they tell me otherwise regarding battery degradation I’ll continue to charge to 100% at home on my 7kWh wall box and up to the recommended 80% on public DC rapid chargers, which up until now I haven’t had a dire need to use regularly.

No-one will tell you otherwise. You'll just end up with a battery that will degrade faster than one cared for in a more forgiving manner.

The battery warranty will kick in if it drops below 70% health. Its very unlikely to get that bad within 8 years even charging to 100% every day. However, you may find that after 8 years and 100k, a battery thats been treated nicely might have 10% deg and your battery has 20%. Made up hypothetical numbers ofcourse, but at the end of the day, the fully charged battery WILL degrade more than the one that isnt. Exactly how much depends on many factors.

I suspect a lot of folks wont give a crap because they'll only keep the car 3 or 4 years. I tend to keep my cars much longer, so i'll do what i can to keep it healthy.

[NickyP]

Interesting topic which makes me wonder what these cars will be worth in 8 years time.
Personally I wouldn't touch an electric car of that age for fear of the battery failing at great cost no doubt.

Anyone feel the same or am I way off?

[Goaty]

Interesting topic which makes me wonder what these cars will be worth in 8 years time.
Personally I wouldn't touch an electric car of that age for fear of the battery failing at great cost no doubt.

Anyone feel the same or am I way off?

In the ‘old days’ all you could really go by was number of owners, mileage and service history. In addition to all this, I’m not sure how someone can determine what the battery will be capable of after ~8 years. Maybe there will be some sort of service which can download the car’s entire charge history and ‘advise’ according to how often it was fast charged, left sitting for days at 100% etc. I suppose that data may be held somewhere in the ‘black box’ equivalent?

[Erakettu]

With an OBD tool you can see amount of AC and DC charging as well as some estimate of battery degradation. One can also test battery capacity themselves at a charger to get a rough estimate. There are commercial services for this also, which I guess will be more popular over time.

I think it's a bit selfish not to care about the battery life even if you plan to keep the car for a short while. The battery consists of precious resources and any waste here is an isult on sustainability.