Charging: Less is More

Everyone has done it: after the pump clicks off at the gas station, we squeeze the lever 2 or 3 more times. Trying to coax that extra half gallon into the tank to make sure we are more than full and have the most possible fuel in the tank.

The issue is this same behavior follows people when they buy an EV. They always try to charge to 100%n when traveling on long trips filling up at Fast Chargers (DCFC). Looking it this only from the context of how long it takes to charge, when the battery nears full the car slows down, or tapers, the charging to protect the battery.

You should charge regularly to 100% at home, to ensure a function called cell balancing occurs to make sure all battery cells are charged to the same level. This process takes a long time to complete, so the car needs to be charged fully on a regular basis to ensure this happens (doesn’t need to be every charge, and this will be a topic for another day).

Back to DCFC, Each car is a little different with how the charge tapers off at the end. My older 2015 BMW i3 slows its charge rate dramatically after it is about 75% full, but the newer models with larger batteries don’t slow down much until they reach 95%. What this means is my older i3 charges quickly to 0-75%, but very slowly from 75-100%. Taper is the downward slope of these graphs, and you notice above 80% the 50 kW max BMW i3 is charging as fast as a Model 3.

What this means is when traveling on your long trips and topping off your Model 3 (charging above 60 or 70%), you are wasting a lot of time, and causing more stress to your battery. The fastest and best for your battery option is to drive it as low as you feel comfortable, then charge it up to only 60 or 70%, making sure to have a comfortable range to make your next stop. This will work better with Model 3 Long Range, the Standard you might have to top off. The Audi e-Tron can charge to 80% before getting taper, although it has good taper characteristics.

This method of avoiding the taper means having more frequent but much shorter charging stops. Instead of taking 1 hour to top off you stop for 20 minutes and go. With Supercharging V3 it is even more true, the car will charge so rapidly from the 20-60% range you will hardly have time to buy a coffee and use the facilities.

Using the nice trip planner at https://www.evtripplanner.com (I have no affiliation), with the Model 3 Long Range it shows that if I try to drive my 800 mile trip in only 2 stops (start full, and charge to full twice ending empty), it will take 40 minutes longer than if I stop 4 times, but only charging to 60% or so. This is because the Model 3 charges much more rapidly from 20-60% than from 60-100%.

Save some time by not charging to full (as long as range and conditions allow).