Best way to do L3 charging for speed and battery health

I noticed when I charged my 2017 Leaf on an L3 for the first time (briefly) that it appeared to charge at 40KWh then dropped down to 20KWh (might have gone further but I was just testing it). Is that a feature of the way that the charger reports or a real thing?

I just read, "When the vehicle battery's SoC is below 20 percent or above 80 percent, a DC fast charger's charging rate slows considerably" https://www.caranddriver.com/shopping-advice/a32600212/ev-charging-time/ .

If I have the choice then (if there are fast chargers at close enough intervals) would it be fastest on a long journey to charge from 20 (+) to 80% when I get the chance? Or just to charge from 20(+) to whatever charge would safely get me to the next charger? Would it make any difference to the overall speed I charge at?

It depends completely on the DC fast charger and how aggressive it is. That's not how it is suppose to be, the car is talking to the QC and telling it how much power to send, but I've noticed that depending on the QC network you choose, that can very greatly from "cautious to melt the battery" as far as how fast it will charge. It is true, most QC will ramp up power past 20% and then after 50% you start to see it ramp down slightly and then quicker the closer to 80% that it gets and beyond.

The first annoying issue I've noticed at QC is that whatever max they have in power output, they gauge that for the ramp up and ramp down. So even though most of the QC will advertise 50 kW, they may only have a 40 kW or 45 kW true max, some as low as 30 kW (*cough* Nissan Dealerships *cough* ) and thus seem to take a long time. Unless you have a lot of different QC networks around you to compare, you'll never notice this at the same QC you visit all the time.

Example, Electrify America, seem (at least where I am) to have super aggressive QC stations. I can bring my 2013 Leaf at 72F battery temperature, say 20% charge and do a QC session that will hammer the battery with 50 kW all the way to 80% and then continue 20 kW all the way to 100% and the battery is sitting at 110F. If I were to duplicate the car conditions again the next day at a Blink QC, same battery temperature, charge level, etc. It will only max at around 44 kW and well before 80% it is already down to 20 kW and finally finish up at 6 kW to top off at 100%, thus taking a very, very long time to finish. But.... the battery temperature will only be raised to 90F for that session, thus probably less wear and tear on the battery.

For your situation, I would recommend enough to get from one QC to the next because as the battery temperature keeps increasing, you notice lower and lower charge power each time. You also don't know how aggressive one QC to the next will be and thus you might spend a lot of time at a QC if it has a very "cautious" approach to battery charging when the temperature is higher.

Your car will always slow down as it fills. The general thought for DCFC (L3) is to do it to 80% as you say and move on unless you really have to. For long trips sometimes I really have to. It is usually cheaper to move to an l2 after it hits 80.

On health I wouldn't worry too much. Some say don't DCFC too much and you clearly do not. The LEAF has a hard time cooling so repeated fast charges build up heat that the LEAF has trouble getting rid of, this is because it has no battery cooling system. Overall I wouldn't worry too much unless you are trying a really long trip. I actually suspect DCFC does not do much to battery health but too much prolonged heat does (see Arizona LEAFs). DCFC can contribute heat but unless you are doing repeated DCFCs I wouldn't worry. Just drive the car, use the DCFC.

What I suspect is more important is not letting the car sit too empty (like below 20) or too full like 90-100 for too long. I see lower health scores from cars that have done that.

drbrake said:

I noticed when I charged my 2017 Leaf on an L3 for the first time (briefly) that it appeared to charge at 40KWh then dropped down to 20KWh (might have gone further but I was just testing it). Is that a feature of the way that the charger reports or a real thing?

I just read, "When the vehicle battery's SoC is below 20 percent or above 80 percent, a DC fast charger's charging rate slows considerably" https://www.caranddriver.com/shopping-advice/a32600212/ev-charging-time/ .

If I have the choice then (if there are fast chargers at close enough intervals) would it be fastest on a long journey to charge from 20 (+) to 80% when I get the chance? Or just to charge from 20(+) to whatever charge would safely get me to the next charger? Would it make any difference to the overall speed I charge at?

Click to expand...

Below 10% SoC is asking to get stranded; above 90% SoC is **slow** charging
In between it is ONE HUGE YMMV, and in your LEAF you probably do not have much leeway to choose anyway.