Technical question on charging to 100%

Technical question on charging to 100%

Suppose you have to travel, and for one reason or another you reckon 100% charge will be necessary or at least advisable.

You could charge to 100% at night and leave it plugged in. But is there any advantage to charging to 90% during the night, and topping up to 100% in the morning?

My logic is, there could be a few factors that apply.

a) Perhaps electrode degradation happens not only when charging, but also when the battery sits at full charge. Keeping the time it sits at 100% could have some effect.

b) Keeping the temperature down is good for batteries, especially towards full charge. So letting the bulk of the battery cool down, then putting in the last 10% could have some effect as the battery would start cool and then gradually warm up, maybe not to as hot as if you did it all in one go.

c) A warm battery is better for driving, so they say. So doing the last bit of charging in the morning could leave the battery nicely warmed up and ready to go, whereas doing it at night would give you a hot battery when you don't want it, which would be cold by the morning. Also, having only just now charged up to 100% there might be a joule or two more in there.

d) Of course, if it's hot/cold out there you can cool/heat the cabin while it's charging too.


bishoppeak | January 11, 2019

If you've got the time, it sounds OK. Better for the battery than leaving it at 100% overnight. That 10% will take a long time though, so pack your patience.

RAR | January 11, 2019

Charge directly to 100%, but start the charging cycle so that it completes just before you plan to start driving.

If you don't know how long it will take, start it early, and see what charge duration the car lists for completion. Then stop that charge cycle, and program it to start at the appropriate time.

I do this often to avoid an intermediate stop after breakfast at home, and get to a farther supercharger for my first stop of the day before I need a comfort stop or food break.

barrykmd | January 11, 2019

When I charge to 100%, I usually charge to 90 when I get home the day before and do the last 10% early in the morning before leaving.

avesraggiana | January 11, 2019

What @barrykmd said.

I set the charger to start charging at 0000 hrs, to 90%. Whenever I wake up, I reset the charge to 100% and restart the charging.

It takes me about 90 minutes to get ready. On a Tesla HPWC at 72 amps that last 10% takes about an hour. By the time I climb in, the car will have sat at that very high 100% charged state for no more than 30 minutes. No harm done.

rxlawdude | January 11, 2019

@aves and @barry +1

Anthony J. Parisio | January 12, 2019

Remember the longer a Lithium battery sits at 100% the greater chance that dendrites will form and short more sections of each battery. The more often this happens the sooner you pack will die. One Youtube mostly filled to 100% and mostly at superchargers. He often would come close to 0%. His battery pack had to be replaced before 150,000 miles. Tesla blamed him for misuse of the battery.

jordanrichard | January 12, 2019

Don’t let the battery sit at 100% for any longer than necessary and in your scenarios, it isn’t necessary. As already suggested, charge to 90%, then change the SOC level to 100%, see how long it says it will take, subtract that from when you plan on leaving the next day and set it to start charging at that time, leaving it at 90% for the night.

jjchan.OH.US | January 12, 2019

I use an iPhone app EV ChAmp to take the guessing out. You dial in the time you want the car to reach 100% charge the night before, enter the starting time, and the app tells you what amperage to set your car at. It gets really close. App is free, BTW.

shred86 | January 12, 2019

I will typically set my charging to finish about 30 minutes prior to leaving, mostly so the battery is closer to optimal temperatures and to have full regen braking. When I get home, I'll plug in the charger and see how long it will take to finish. From there, I'll just set a charge schedule to finish about 30 minutes before I plan on leaving. It would be nice if you could simply set a "finish charging time", which I can't imagine being very difficult for Tesla to implement.

tes-s | January 12, 2019

You are overthinking this.