We own EVs. Ask Us Anything.

[SpaceEVDriver]

We went to Trader Joe’s yesterday. It’s about 100 miles from my house. I was thinking today I’m going to start tracking my longer trips and the places I go and if the BEV would work. Typically when I go up towards Chicago I get gas either halfway there or halfway back. I decided not to get gas yesterday. I started with 300 miles. I am down to 84 left. Now I need to go get gas, but if that was the BEV I could just plug in. Lots to consider.

Just to make sure I have this right, you charge to 80% when at a charging station, but you can charge to 100% on your home charger?

Thanks for answering all my pesky questions!

Storage of a battery at 100% is not great. Maybe. But that's storage for months, not hours or days, and at very high temperatures. That said, an EV battery will never reach 100%. Every modern EV battery manufacturer programs its battery management modules to keep the battery below 100% charge. My battery has 143 kWh maximum capacity, but can never charge past 131 kWh (91.6%) capacity. When the UI reads 100%, it's at 91.6% actual. When it reads 80%, it's 73% of actual.
I don't worry about charging to 100%, but usually keep the home charge set to around 85-90% and tell the vehicle to go to 100% shortly before a long road trip. In the winter, I'll do this such that the battery is slightly warmed before the trip. In the summer it doesn't really matter so I'll charge to 100% whenever I remember to do so before the trip.

There are two reasons I don't usually charge to 100% at home: 1) I live where the temperatures fluctuate enough that I like the battery to be able to thermally respond without any possible issues. This is a holdover from my experience with batteries in space where fluctuations matter a lot. Extreme temperatures in space aren't what we see on Earth, but it's difficult to let go of this even though it's not a huge issue; 2) because it's slightly more efficient to drive with less than 100% charge. Regeneration doesn't work as well when the battery is at 100%---you can't pour more than 100% into a container.

I will charge to 100% before a long trip. The slight improvement in efficiency isn't as important because I'm on a highway and don't expect a lot of regeneration for most of the drive. Also, while on a long trip, I usually use the DC chargers to get just enough to make it to the primary and a secondary charging station. I like to drive about 2.5-3 hours at a time, which gets me 180-220 miles, and uses up to about 70% of a charge. So I usually plan legs of about 150-200 miles. I don't like to sit for more than about 2.5-3 hours at a time.

Most vehicles reduce DC Fast Charging rate when the battery reaches 80% or so. The Lightning, for example, will go from about 150-175 kW to about 80 kW when it gets to 80%. It drops again after about 85% to 50 kW. So, DCFC charging above 80% is about half as fast as charging below 80%, and charging above 85% is about 2/3 as fast. So, if your next charging stop is within a few minutes off your route, you can save time by stopping charging at 80% to 85% and moving on.

Regarding battery health:
The major control on battery health is age.
The next, much lower down on the impact scale is long-term storage at a combination of high state of charge (90%+) and high temperature (50+ ºC). Pretty much nobody does this.
The next is how much of a charge happens how quickly. It's best to always be plugged in at home so that you get short charges. That is, plug in after your 40 mile commute to recharge 11%; that's better than waiting until the end of the week to recharge 50-60%. You can't avoid large charges when you're traveling. But don't worry about it, the evidence is that batteries are going to outlast the rest of the vehicle.

 

[oldgeeksguide]

My understanding is that it's better for long term battery health to charge to 80% regardless of where you are charging. If you need the extra range for a long trip it shouldn't hurt to occasionally charge to 100% but for your normal driving you likely wouldn't need to and 80% would be plenty.

I think it’s not as strict as that. I’m no battery expert, but from what I gather it’s more like you don’t want it at sitting at 100% all the time, you don’t want it to sit at 0% for very long, so generally keeping it between 20%-80% is a good rule of thumb. It doesn’t hurt to charge it all the way to 100% periodically, and if you drain it to 0 you should start charging it again asap. Slow charging tends to be easier on the battery, but fast charging shouldn’t hurt too much as the battery management systems are pretty good.

One caveat, if you’ve got LFP batteries (like the harvester), they like to be at 100% more, so it’s helpful to charge them fully more often.

But overall, you shouldn’t have to think about it much.

 

[Cranky Canuck]

Others have left excellent comments about maintaining battery health, the one thing I'd add is that while it's a good idea to keep the battery between 20-80% for daily use, it is necessary to charge to 100% some of the time to balance the battery cells. Hyundai recommends I charge my Ioniq 5 to 100% at least once a month "to maintain battery health". That's so that the battery management system is able to balance the cells. It usually works out that I do that anyway because I do a long trip about once a month but it's something to keep in mind.

Basically charging to 100% doesn't hurt the battery, you just don't need to do it every day.

Fast charging is can also be good for the battery too. I was speaking with an actual battery expert the other day (he worked on batteries for satellites) and he said it's good to occasionally hammer the battery with current sometimes as it seems to zap the dendrites that build up in the cells over time. He was saying they built a special circuit with a capacitor into their satellite to essentially serve this same function where it would periodically zap the battery pack to "burn off" the dendrites. I'm not a battery expert but he seemed to know his stuff and I've heard that from other sources as well so don't be afraid to fast charge either.

Essentially these vehicles are designed for consumers and you really don't need to know all this stuff. Just use them normally and charge them when/how you need to and you'll probably be okay.

We're just some EV nerds that like to know how things work. Same as petrolheads who like to talk about advancing the spark timing and stuff. Most people don't need to know or care about that stuff.

 

[SpaceEVDriver]

He was saying they built a special circuit with a capacitor into their satellite to essentially serve this same function where it would periodically zap the battery pack to "burn off" the dendrites. I'm not a battery expert but he seemed to know his stuff and I've heard that from other sources as well so don't be afraid to fast charge either.

I work on satellites that explore the solar system. And, yes, we do have several tricks to make batteries last a lot longer. But mostly it's because we're operating $B machines that can't be brought back to the shop for repairs. These tricks are necessary in part due to the the very large temperature swings and gradients these machines experience. Some spacecraft can experience temperature gradients between 40 Kelvins (-233 ºC) and 700 kelvins (427 ºC) across just a few meters. The batteries can be abused so much that it's sometimes surprising to me that we still have spacecraft operating on battery power after decades and decades. We also have rovers on Mars that are running Li batteries with very large temperature swings and charge level swings. They do have different chemistries than we have in our vehicles here, but they're also abused a lot more than we see in our vehicles here.

Essentially these vehicles are designed for consumers and you really don't need to know all this stuff. Just use them normally and charge them when/how you need to and you'll probably be okay.

Exactly. Just plug in whenever you can, drive how you want, and enjoy your car. It's time for the FUD about batteries to go away.

 

[J Alynn]

Others have left excellent comments about maintaining battery health, the one thing I'd add is that while it's a good idea to keep the battery between 20-80% for daily use, it is necessary to charge to 100% some of the time to balance the battery cells. Hyundai recommends I charge my Ioniq 5 to 100% at least once a month "to maintain battery health". That's so that the battery management system is able to balance the cells. It usually works out that I do that anyway because I do a long trip about once a month but it's something to keep in mind.

Basically charging to 100% doesn't hurt the battery, you just don't need to do it every day.

Fast charging is can also be good for the battery too. I was speaking with an actual battery expert the other day (he worked on batteries for satellites) and he said it's good to occasionally hammer the battery with current sometimes as it seems to zap the dendrites that build up in the cells over time. He was saying they built a special circuit with a capacitor into their satellite to essentially serve this same function where it would periodically zap the battery pack to "burn off" the dendrites. I'm not a battery expert but he seemed to know his stuff and I've heard that from other sources as well so don't be afraid to fast charge either.

Essentially these vehicles are designed for consumers and you really don't need to know all this stuff. Just use them normally and charge them when/how you need to and you'll probably be okay.

We're just some EV nerds that like to know how things work. Same as petrolheads who like to talk about advancing the spark timing and stuff. Most people don't need to know or care about that stuff.

That’s great info. Based on that conversation would it make sense for SM to consider adding a capacitor to do as you heard regarding the satellite? Knowing dendrites are one of the biggest harms to battery use-maybe it would be worth adding that as not everyone will want /need to fast charge very often. That cool insight from that engineer

 

[SpaceEVDriver]

That’s great info. Based on that conversation would it make sense for SM to consider adding a capacitor to do as you heard regarding the satellite? Knowing dendrites are one of the biggest harms to battery use-maybe it would be worth adding that as not everyone will want /need to fast charge very often. That cool insight from that engineer

I don’t think that’s worth the cost and entirely not necessary for an Earth-bound battery. A 1-2C recharge rate from time-to-time will take care of the battery health just fine.

 

[Cranky Canuck]

That’s great info. Based on that conversation would it make sense for SM to consider adding a capacitor to do as you heard regarding the satellite? Knowing dendrites are one of the biggest harms to battery use-maybe it would be worth adding that as not everyone will want /need to fast charge very often. That cool insight from that engineer

I would say no, probably not worth it. They did it (the person I was chatting with has been retired for a while so admittedly his information is likely a bit out of date) because as SpaceEVDriver said, you can't just bring a spacecraft in for repairs, you need to guarantee it will work. I don't think capacitors or anything like that will be necessary to burn off dendrites in car batteries. The engineers of spacecraft take a more 'belt and suspenders' approach because that equipment is being used at the bleeding edge where cost, and weight are huge factors along with the environmental extremes.

For cars they usually build in a bit of redundancy into the pack to account for the loss of a few cells to dendrites over the life of the vehicle. That's in there with the "hidden" top end capacity people talk about. The occasional fast charge might also help deal with them. Either way it's likely unnecessary to build in such a system as SpaceEVDriver just said.

 

[J Alynn]

I don’t think that’s worth the cost and entirely not necessary for an Earth-bound battery. A 1-2C recharge rate from time-to-time will take care of the battery health just fine.

Thanks

 

[J Alynn]

I would say no, probably not worth it. They did it (the person I was chatting with has been retired for a while so admittedly his information is likely a bit out of date) because as SpaceEVDriver said, you can't just bring a spacecraft in for repairs, you need to guarantee it will work. I don't think capacitors or anything like that will be necessary to burn off dendrites in car batteries. The engineers of spacecraft take a more 'belt and suspenders' approach because that equipment is being used at the bleeding edge where cost, and weight are huge factors along with the environmental extremes.

For cars they usually build in a bit of redundancy into the pack to account for the loss of a few cells to dendrites over the life of the vehicle. That's in there with the "hidden" top end capacity people talk about. The occasional fast charge might also help deal with them. Either way it's likely unnecessary to build in such a system as SpaceEVDriver just said.

Thank you sir!