Battery Life and DC charging

One of the questions we often hear is "But doesn't DC charging damage the battery?"

As far as we can make out the answer is "No. Really. No."

Now we're not battery chemists and we're not car manufacturers, but we read what other people have published and we see the articles that have actual data. So since we keep getting asked we gathered the various things we'd read into one place.

While there are many articles on the internet reporting what someone said to someone else at some stage somewhere, the actual data suggests a few things.

• If there is a difference, it's small

• If there WAS a difference it was in early EVs. (like 2012 Nissan Leafs)

We might add one other conclusion.

• Some battery degradation happens no matter how you charge the EV, but it's not a big deal. It kinda used to be a big deal in very early EVs. But it isn't any more. So stop worrying about it.

The published articles that seems to us to have real data are two.

1. The Recurrent Auto article here

   1. Note: This is based on their data on REAL charging of more than ten thousand Teslas.

   2. Their conclusion is nicely summarised in these two sentences.

      1. "Instead, to our surprise, our analysis of more than 160,000 data points found that there was no statistically significant difference in range degradation between fast charging more than 70% of the time and fast charging less than 30% of the time."

      2. "In short, the robust thermal, voltage, and battery management systems that EV makers have invested in do protect their batteries from damage with routine fast charger use. ‍"

   3. They do caution that high speed charging in extreme temperatures (hot AND cold) can have an effect. But we're talking extreme North American continential hot and cold temperatures.

   4. The current version of the article doesn't include the nice charts that the original version had. The original version is here and is included in its entirety at the bottom of this page.

   5. This chart in the old article is probably the best summary of the whole thing. Click on the link...it's likely to be a surprise.

2. The Idaho National Laboratory in the US did a study on 2012 Nissan Leafs

   1. The results were published in 2015. So this study is on early generation cars.

   2. The report stresses that their DC charging cycles were VERY intense. They fully charged the cars at max speed twice a day. In the heat of the US Southwest.

   3. They saw a difference of approx 3% - 5% between cars that were charged DC vs cars that were charged AC.

   4. They describe this difference as an upper bound.

   5. They point out that batteries, battery management systems, and battery thermal management systems are improving all the time.

   6. A 2012 Nissan Leaf is an antique.

      1. It's really dramatic how much more the batteries degraded - in all charging cases - in these old Leafs compared to the levels in a more recent vehicles. The batteries degraded easily twice as much.

Some AC charger manufacturers still quote the Idaho study. Mostly without saying how old it is. I don't know of anyone in the EV world who would claim a 2012 Nissan Leaf as being representive of modern EVs.

There's also a wide-ranging GeoTab article here which does point out that DC charging in hot climates - again in the USA - does have some impact. A few percent. This article is sometimes quoted without those caveats. Also, unlike the above two articles, GeoTab really don't give much information on the data source. The data used does seem to include some older vehicles.

But the main conclusion of the GeoTab article still seems to us to be "The battery won't wear out before the vehicle does so stop worrying about it".

There was also a study by a UK university, using funding by the UK govt, which came to the same conclusion - that DC charging did no meaningful damage to the battery- but the report link has been removed. Or at least the link we had. If we find the report again we'll put it here.

So, that's what we know. Other articles tend to have urban myth quoting other urban myth and not much more. As far as we know, DC charging of modern vehicles is fine. There may be an impact of a couple of percent of battery over several years, or no impact at all. Either way it's a marginal point.

So to repeat our main conclusions:

• If there is a difference, it's small

• If there WAS a difference it was in early EVs. (like 2012 Nissan Leafs)

One additional point of speculation on our part is also that if there is any effect at all, it'll be even closer to zero in 800V vehicles. Higher voltage, less current. Less current, less heat. Less heat, easier for the battery management system and thermal management system to keep everything tidy.

Thanks for your time!

---

Here's the original Recurrent article with the charts included.