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Charging to 100%: Frequency Question

Charging to 100%: Frequency Question

I work in two offices that are 93 miles apart (Norfolk and Wallops Island, VA). My round-trip commute when I work in our Wallops office is 186 miles, three to four days a week. It's a rural, isolated area, so there are no superchargers or destination chargers along the route. On a warm or mild day, I can make the round trip on a 90% or 80% charge, with plenty of juice left over. On colder days, obviously, I suffer some range loss. (Yesterday, for example, I started with 283 miles of range and was down to 47 when I got home. Average temperature was 40 degrees). 99% of the drive is highway miles, and I only experience 1 or 2 miles of phantom drain when the car is parked.

So, to hedge my bet, I like to charge to 100% on cold days. I use Scheduled Departure, so charging stops roughly fifteen to twenty minutes before I leave in the morning. I've read so many differing opinions on when to charge to 100%, how often one should, or questioning whether one should at all, that I'm rather confused. What's the best practice here? Am I okay charging to 100% a couple of days a week as long as I'm on the road shortly after charging is complete? Am I shortening the battery life by doing this? I plan to bat my eyelashes at my employer and push for a couple of destination chargers in our parking lot, but that will be a long way off, and Winter Is Here.

jrweiss98020 | January 8, 2020

Charge it when you need it!

There's no question that the battery life is finite, but nobody can predict exactly how much capacity YOUR battery will lose in what time frame. Some might argue that you should charge to 100% every day, in hopes it dies before the warranty expires, and you can get a new battery free...

jordanrichard | January 8, 2020

die7fox, as long as you start driving shortly after it reaches 100, which you said you do, then you will be fine. Here is what will kill your battery. Starting at about 10% SOC, supercharging all the way to 100, then drive it back down to 10%, then charge back up to 100, etc. etc. This isn't giving the battery a chance to cool down. You are comparatively trickle charging at home which is much better for the sake of heat build up in the battery and Li-ion batteries don't like excessive heat.

die7fox | January 8, 2020

@jordanrichard: Thanks! Yeah, I've only supercharged a few times, and that was on a road trip from Virginia to Massachusetts and back. All of my daily charging is through a Tesla wall connector, and when I charge to 100%, I'm on the road within half an hour of it topping off. I also don't start charging right away. Since I use Scheduled Departure, charging doesn't start until around 1:00 in the morning, even if I plug it in around 6 PM the night before.

gballant4570 | January 8, 2020

die7fox, it is also fair to point out that Tesla battery tech and temperature control systems have improved over the years, and supercharging does not hurt the battery as much as it did when all this got started. If charging to 100% bothers you, go ahead and supercharge when you need to!

But I would also say your 100% charging methodology is quite sound. I do something similar when anticipating a high mileage day, but since I don't leave early I do a 90% to 100% charge before driving, starting the drive immediately after the top off charge.

andy.connor.e | January 8, 2020

Why does it feel like this is the 5th thread we are answering the same question to.

Pg3ibew | January 8, 2020

@andy, this seems like the 5th, because you probably missed the other 15.

Frank99 | January 8, 2020

Charging to 100% daily will indeed shorten your battery life. It's just the chemistry of the battery. How much it shortens it is unknown. I expect that at 200,000 miles, my battery will have between 90 and 95% of it's original range - by daily charging to 100%, perhaps yours may be down to 85% (or 80%; or 89%; we just don't know). Some suggestions:
1. Classic Tesla cold-weather approach - use the seat heaters rather than the cabin heater for comfort; set the cabin heater only as high as you need to be comfortable with the seat heaters on. Pre-heat the car before you leave using wall power; I don't think that's possible if you're using scheduled charging, however.
2. If your employer has any 120V outlets near where you park, ask if you can use them on cold days. 9 hours at a 5 miles/hour charging rate would add 45 miles of range.
3. If you can get by with a 95% or 90% charge, I'd strongly recommend it.
4. If you're running short on charge on the way home, drive slower.

If ya gotta charge to 100% on cold mornings, ya gotta. Your approach of timing charging so it ends just before you leave in the morning is the right strategy for minimizing any degradation that might occur.

vmulla | January 8, 2020

OP,
I have a similar commute of 176 miles between Northern Virginia and Baltimore, and I too take rural roads where there are no Superchargers to replenish charge (there are 2, but both are too close to my destinations to consider them)
I charge to 100% if I notice cold and wet conditions, but I make that determination after I wake up, the car is charged to 90% anyway. I head out with more than ~95%. With 90% charge I was down to ~40 miles in the worst of conditions (slush+low temps) - so I'm really pushing the charge past 90% only to feel safe, much like you. Your commute distance is close to mine, so maybe you can try my strategy?
I've charged the car to 100% several times even on Superchargers without any ill effects (that I can tell)

andy.connor.e | January 8, 2020

@Pg3

ha

die7fox | January 8, 2020

@vmulla: Thank you! That's helpful.

gballant4570 | January 8, 2020

Batteries have an estimated lifetime measured in charge cycles. Today's tech is somewhere in the neighborhood of 1k-2k charge cycles. Of course the charge cycle is from empty to full, so charging your Tesla to 100% does not actually constitute a charge cycle.

So long as your battery does not sit on a full charge, especially routinely, and so long as the temperature of your battery is managed well - both during charge and discharge cycles, the lifetime is mainly driven by those charge cycles. The size of the battery times the charge cycles will equal a number of kwh. That number of kwh is easily converted into miles. If you are driving a lot of miles, you will use more kwh. If you use more kwh, you'll need to charge those kwh back into the battery.

If you do not harm your battery along the way (temp control and dendrite formation from sitting on a full charge), your charging habits will not significantly change any of that.

Bottom line is, battery life can be measured in miles. Miles can be converted to kwh, and kwh determines # of charge cycles.

die7fox | January 8, 2020

@gballant4570: Thanks! I'm not well-versed in the technical aspects of the batteries, so this was instructive.

andy.connor.e | January 8, 2020

1500cycles * 75kWh * 4.13miles/kWh

~464,625 miles.

andy.connor.e | January 8, 2020

1000-2000 cycles gives you a variance between

309,750 - 619,500 miles

So longer than pretty much anyone would keep a gasoline car.

die7fox | January 8, 2020

@Frank99: There are 120v outlets on the exterior of the building, and I've been told that I can use one if the need arises. Even twenty or thirty extra miles of range would be welcome on days where I think I might be risking it by not charging to 100%.

andy.connor.e | January 8, 2020

Also consider slowing down on the highway to preserve range. You dont get there that much faster going 5 or 10mph over the speed limit, but you save an exponential amount of energy.