In November, I purchased a 2019 Bolt EV with DC fast charging capability and have just had my first experience using that feature. With outside temperatures in the 40's, I used a nearby EVgo fast charger for a half hour and according to a follow-up e-mail from EVgo, the energy charged was 11.6 kWh. From the Bolt's instrumentation, it appears that a half hour's DC fast charge added slightly more than a 1/8 increment to my battery charge level and extended the remaining range of my current charge by around 40 miles. For my future expectations, I am wondering whether that experience is pretty typical from the Forum's actual experience. Any input appreciated - thanks!
I did not think to check the rating of the EVgo charger I was using. My Bolt had slightly under a 1/4 charge when I plugged into the DC fast charger. The half hour's worth of fast charging got the charge to around halfway between the 1/4 and 1/2 charge marks.
Your experience isn't the typical experience, but it certainly has been experienced by others.
11.6 kWh in 30 minutes means a charging rate of about 23 kW. Gaining a bit over 1/8 of the battery means that the rate at which charge entered the battery averaged out to be about 16 kW. Either way, that's much less than half the charging rate the Bolt is capable of. So, let's talk about why this happens.
Although the car is capable of charging at 150A, but it will limit current based on battery temperature (and state of charge). We actually know a little about how it does that (source
- -30.0 ℃ / -22 ℉ — 0 amps, car will not charge at all until battery has warmed
- -20.0 ℃ / -4 ℉ — 3 amps, very slow (1 kW, slower than home charging from a 120 volt outlet)
- -10.0 ℃ / 14 ℉ — 12 amps, slow (4.3 kW, slower than typical level-2 home charging)
- -0.0 ℃ / 32 ℉ — 30 amps (10.8 kW, finally faster than home charging)
- 10.0 ℃ / 50 ℉ — 54 amps (19.4 kW)
- 15.0 ℃ / 59 ℉ — 93 amps (33.4 kW)
- 22.5 ℃ / 72.5 ℉ — 134 amps (48.2 kW)
- 25.0 ℃ / 77 ℉ — 150 amps (54 kW, faster than almost all DCFC chargers can supply)
- 40.0 ℃ / 104 ℉ — 150 amps (54 kW, faster than almost all DCFC chargers can supply)
- 45.0 ℃ / 113 ℉ — 75 amps (27 kW)
- 50.0 ℃ / 122 ℉ — 0 amps, car will not charge at all until battery has cooled
We can visualize this as the following graph:
Note, however, that (unlike the Leaf and the American edition of the upcoming Hyundai Kona, the Bolt can also heat its battery, but there is a lot of thermal mass to the battery, so it takes a while for the heater to raise the battery temperature). Thus, if you'd stayed longer, you'd have seen charging speed pick up a bit as the heater got the battery warmed up.
If we assume that the interpolation line I drew between the known points mirrors reality, at battery temperature of 45 ℉ you would have only charged at 46 amps (16.6 kW) initially. If your car had been sitting in the cold (e.g., overnight without being plugged in), it's possible that your battery was even colder.
On the other hand, driving the car warms the battery a little, and the battery has a significant thermal mass, so it's very possible for it to be 45 ℉ outside and have the battery be significantly warmer.
From your description, it seemed like you were using a DCFC charge as an experiment to test it out (and were disappointed).
In a more typical cold winter trip scenario, it'd go like this. You'd charge the car overnight while you slept. As part of the charging process after the battery is charged (which generates some heat all by itself), the car will automatically run the battery heater to raise the temperature closer to a good temperature. Before setting out, as you ate breakfast and got ready to leave, you'd use the preconditioning feature to warm the car up with wall power before setting out. One 30 minute session is great, two would ensure the car is as warmed up as can be. Preconditioning will further make sure that the battery is brought up to a good temperature.
During the trip, a mix of the thermal mass of the battery retaining the heat from preconditioning and the heat generated from using the battery will keep it at a good temperature so that when you arrive at your first charging stop you'll be well placed to charge at a good rate. The charging process will further raise the battery temperature so that further driving and charging will always see good speed.
Put simply, EV batteries don't like the cold. There are things you can do to help, but it's also possible to be caught out. It's true for all EVs. There are frustrated folks on Tesla forums, too, for example.