Best charge level when charging the day before a long trip and not able to schedule charge overnight?

[J-a-x]

My building has a shared leve2 charger and I'm not allowed to charge from 7 am to 9 am so it's hard to charge overnight without being inconvenienced in the morning. I want to leave for a road trip at 10 am. Rather than leaving it charging overnight and waking up at 7 am and moving my car I'd prefer to charge it the day before and stop charging before bed then return to the car in the morning.

I know charging to 100% and leaving it is bad, so that seems out of the question but I also want to maximize my range the next day.

What's the best charge leve to 1) protect the battery while it sits overnight and 2) maximize range the next day? I assume charging to 100% the night before the trip and letting it sit for 10 hours at 100% is bad and I should not do that but does it make a difference if its going to be very cold at night and I expect some discharge before my trip? If I charged to 100% it wouldn't really sit at 100% for 10 hours, it would slowly discharge due to the cold.

Is it better to charge to 100% then let it sit for 10 hours where it may discharge by a percent or two, or to charge to 90% then wait until 9 am to move it back to the charger at 88% and charge again right before the trip? This is less convenient but maybe safer for the battery? My worry however is if I do that it won't charge fast since it'll be cold but may be the safest option. What is the best charge level to use in this situation?

I sure am looking forward to getting my own charger at my parking space!

 

[RTPEV]

I like to baby my battery probably as much as anyone, but I wouldn't stress too much about charging to 100% the night before.

But, do you have an option to plug into 120V to top off overnight? Does your car have LFP battery (in which case there is little concern anyway)? Can you charge to 90% and then top off between 9-10am? The battery is a big thermal mass and may not cool as much as you fear overnight. Finally, determine if a 100% charge is really warranted anyway. If your first anticipated stop is only 80% away, you could easily get away with a 90% charge anyway. Play around with different starting SOCs in abetterrouteplanner.com and see what you really need.

 

[J-a-x]

Thanks for the insight. I live in Boston and plan to go skiing which means a 100 mile drive followed by 7 or 8 hours parked in 20F cold followed by a 100 mile drive home (or a 30 mile drive to the nearest supercharger after skiing if im running low), so 100% before I leave is helpful to avoid a stop on the way out of town and a bit of a buffer during the day. It will be a very cold night (10F) the night before the trip. This will be my first really cold night with an EV so i dont know what to expect about overnight drain yet.

I’m driving a model Y long range which is not LFP battery...

 

[RayK]

If it were me and the route allowed, I'd charge to 90% the night before, leave 30 minutes earlier than "normal", stop at a Supercharger along the way, top off to at least 80% there (the 30 minute buffer), then go skiing. Remaining charge in the battery should last through the day and be enough to get home. If you do this once you should have a good idea if you need to adjust your future trips.

Edit: Reading this now, you may not need to charge to 90% the day before. Just have enough of a charge to get to the Supercharger along the way.

 

[J-a-x]

Yeah if I'm going to supercharge along the way there's a 150kW one about an hour from home and on the way, plenty of time to precondition and stop there for not too long to top off. It's probably the easiest but I like the idea of going straight to the slopes and getting more time skiing because the slopes close at 4 and supercharging after is ideal, which is why I'm trying to plan for ideal charge the night before.

Maybe I just do 95% night before. Then it won't be sitting at 100% but it also won't be dropping below 90 before I leave. Maybe that's the compromise. Then a supercharge after skiing on the way home if there's too much drain during the day.

New forecast says 7F overnight in Boston and -3F when I arrive at the mountain.

 

[beatle]

Just charge to 100% the night before. The battery isn't truly "full" anyway; there is a buffer. While I schedule my 100% charges for the time I plan to leave in the morning, that's mostly so I can leave with a battery that's as full and warm as possible, not to preserve its health.

Plan to stop anyway since it's so cold and you're going up a mountain. When I drove home on Christmas Eve, it was about 8F and I only got 60% of my rated range. That was with a warm cabin, warm battery, and averaging 70mph across a slight decrease in elevation. You might do a bit better since you've got a heat pump, but it's still not magic.

 

[Rocky_H]

The battery isn't truly "full" anyway; there is a buffer.

Not on this version of the car. That was only on some of the rare models that were intentionally locked with less than their real capacity, like the 60 or 70 S and X models that were built with 75 batteries.

 

[J-a-x]

I think both of you are true but just by different margins.

I have a friend who had a really old model S with a software lock preventing him from using the entire battery and he said he alway charged to 100% because the battery had like another ~2x range of capacity that he would never used so he did not care about degradation.

I think even with a car like MYLR that is not software locked, what the car calls 100% is not truly 100% but its closer to 100% compared to the model S example above.

Does my 95% charge seem like the reasonable compromise in this scenario?

 

[animorph]

My normal routine is to charge to 90% at night and then top off to 100% in the morning before we leave. That would be best if you don't want to stop to charge during your trip. Once you've made the trip successfully you'll have a better idea of what to expect the second time.

For longer trips you just need to charge enough to reach the next Supercharger, which probably won't require a 100% charge. Nonetheless, you can save a small amount of time at that first charger by charging to 100% before leaving.

Watch the charge remaining at destination display to make sure you're staying on target. You can always slow down if you're running low on charge.

 

[beatle]

Not on this version of the car. That was only on some of the rare models that were intentionally locked with less than their real capacity, like the 60 or 70 S and X models that were built with 75 batteries.

All cars have buffers. There were software locked batteries as well, but even normal "unlocked" batteries have a buffer of a few kwh. You can see this with a scanning app like SMT and an OBD2 scanner. My 2019 has a 5 kwh buffer.

 

[Rocky_H]

All cars have buffers.

...at the bottom.

My 2019 has a 5 kwh buffer.

...at the bottom.

 

[J-a-x]

No buffer at the top?

So I ended up visiting a supercharger the night before out of convenience (happened to need to do an errand near it), charged to 90, then topped it off the morning before my trip. Didn't get to 100 but got to like 96 before we left, and while topping off got to precondition the battery (it was 12F that day) so it worked pretty well.

According to Eevee app my 99 mile drive cost me 151 miles of range due to the cold. I think I could have (barely) made the round trip on one charge but supercharge was convenient on the way home due to bathroom and food break so I ended up doing that. I'm still glad I nearly maximized my range before leaving. If I had left with <90% charge I would have wanted to supercharge on the way there I think.

 

[RayK]

Do you recall what your SoC was when you stopped to Supercharge on the way back home? That would give you an idea of how much you need to have before leaving home (plus a buffer).

 

[Tronguy]

About the only minor comment on the OP's drive that I'd make is that there's a setting to warm up the car before leaving on a trip. Having a 2018 M3 myself, this is in particular important if one is trying for (relatively) good mileage on a trip. Say one is leaving at 8:00 a.m.; having that departure time set in the car, then having the car plugged in so it can do something about it, say, four or five hours in advance, will have both the car interior (one source of battery drain) and the batteries/motors (another source of excessive drain) up to temp before one leaves.

I think the name for this feature is, "scheduled departure".

 

[beatle]

...at the bottom.

...at the bottom.

Still no problem charging to 100%.

 

[J-a-x]

Do you recall what your SoC was when you stopped to Supercharge on the way back home? That would give you an idea of how much you need to have before leaving home (plus a buffer).

It was somewhere between 25% and 30% but with preconditioning it lost a significant amount of range before it got there compared to where it would have been if I had gone home without preconditioning.

 

[J-a-x]

About the only minor comment on the OP's drive that I'd make is that there's a setting to warm up the car before leaving on a trip. Having a 2018 M3 myself, this is in particular important if one is trying for (relatively) good mileage on a trip. Say one is leaving at 8:00 a.m.; having that departure time set in the car, then having the car plugged in so it can do something about it, say, four or five hours in advance, will have both the car interior (one source of battery drain) and the batteries/motors (another source of excessive drain) up to temp before one leaves.

I think the name for this feature is, "scheduled departure".

yep I did that! I'd be scared to do that without being plugged in though because who knows how much range I'd lose.

 

[Genie]

If you charge to 100% the day before, between sentry mode at night and preconditioning in the mornng you’ll might be around 95% at departure. I would not skip preconditioning on a ski trip!

 

[GtiMart]

Still no problem charging to 100%.

No "problem", the car can, but even the car will tell you that you shouldn't do that often. And we know that it's a bit harder on the battery (apart from LFP maybe) than staying lower. As the title of the thread starts with "best charge level...", it is very valid to suggest not charging to 100% the day before and let it sit there for a long period. You can, the car won't explode, but it is best not to do that.

 

[J-a-x]

I guess the real question this comes down to is: "how long is it ok to let the car sit after charging to 100%".

I know charging to 100% won't break the car, I know it's bad for the battery. I know it's ok (or less bad) if I drive "soon" after charging to 100% but how do I quantify "soon".

If I charge to 100% should I drive minutes later for minimum degradation? Is a few hours later going to make a difference compared to minutes? Can I wait 12 hours or at that point am I causing more battery degradation than say a few hours?