This one came in recently about the best way to minimize long term battery degradation via charging. The driver has two options: frequent fast charging or larger depths of discharge. Knowing that both of these can accelerate degradation, they wanted to know our suggestion.
Dear Recurrent,
I would like your opinion on minimizing my EV battery degradation. Below are the specific scenarios I am trying to compare.
Scenario 1:
My Ioniq 5 is at a 80% state of charge. I drive to work and arrive to the office with 63% state of charge. Later in the day, I leave the office and return home, arriving with a 46% state of charge. I charge my Ioniq 5 at home using my level 2 charger, to 80% (i.e. depth of discharge was 34%).
Scenario 2:
My Ioniq 5 is at a 80% state of charge. I drive to work and arrive to the office with 63% state of charge. But, there is a nearby DC fast charger. I charge my Ioniq 5 to 80%, reaching 200 kW during the 15 min charge (my depth of discharge was 17%). Later in the day, I leave the office and return home, arriving with a 63% state of charge. I charge my Ioniq 5 at home using my level 2 charger, to 80% (i.e. depth of discharge was 17%).
In Scenario 1, I have a larger depth of discharge at 34%, but I use my level 2 charger at home. In Scenario 2, my depth of discharge is only 17%, but I use a DC fast charger.
Which Scenario is better for minimizing battery degradation?
Note: I have 2 years of complimentary DC fast charging at Electrify America, so the DC fast charging is not costing me extra money. Also, I typically commute to work only 1-2 days a week.
Dear Recurrent Community Member,
Thanks for writing!
This is a great question – although a tough one because there's no cut-and-dried answer. I talked to one of our PhD battery scientists and here's the gist of what he said:
The depth of discharge you're referencing isn't actually that low! Generally, it’s considered a low depth of discharge when you fall under 20% SoC (or thereabouts). All the more so because you’re starting at a healthy max charge level of 80%. The round-trip daily usage for your car falls well within a comfortable depth of discharge that should not overly stress your battery.
If you want a refresher on depth of discharge, the recommendation is to limit how much battery you use before recharging for optimal battery health.
On the other hand, we know that with higher charge rates, such as with fast charging, there can be more stress on the battery. But you’re talking about fairly quick charging sessions, during which your vehicle won’t stay at the maximum charge rate 200kW for a particularly long time. This is especially true because the charge rate tends to taper rapidly above 50% SoC. So fast charging in this case doesn’t seem like it would be as bad as it could be if you were going from, say, 10% to 70%, 5 days a week.
Neither of these scenarios poses a grave and obvious threat to your battery longevity. And, the other important thing to remember is that this is your car - using it should be convenient and easy for you. There will be battery degradation over time, but both of these use cases fall into the normal range. The interesting perk in your second scenario is that you’re getting some free charging from EA and saving some of the cost of home charging. If getting some extra savings out of the deal is important to you, that would certainly tip the scales towards topping off at work.
Do you have a question for a battery scientist? Reach out and we may share your inquiry with our community!
