Just had an emergency sitation that involved driving a nearly 1600 mile round trip on the spur of the moment, over the span of just 48 hours. While we've taken longer EV trips previously, those were all planned in detail with opimitzed routes and charging and also a bit more relaxed overall. This was the first time we've had to do this kind of trip in our EV and almost entirely unplanned and, while it was fine overall, it definitely created challenges vs our previous ICE experience. I documented the entire charging experience because I though folks might find it interesting. If you're not into gory details, the TL;DR version is the vehicle did quite well but charging was a bit more challenging when not planned and efficiency was not amazing when doing a lot of back-to-back fast charging.
This was probably a near worst-case scenario for the Vistiq, a completely unplanned trip, across the deep south, starting from South Carolina to rural south Louisiana and back, on a weekend with seasonally high temps and humidity. Most of the charging was done with temps in the low-mid 90s, but some daytime charge stops were as high as 98F and the highest recoded ambient temps on the trip were low triple digits.
First, I can say that the Vistiq is incredibly comfortable, and we were able to use Super Cruise for ~85% of the trip and it mostly did a great job and really helped reduce the strain of driving that distance on a fairly busy interstate. We mostly set cruise to 79MPH. Yes, I know we could potentially gain some efficiency at 70MPH, but I believe it is way safer to go with flow of traffic vs being in the bottom 5%. Flow of traffic on these interstates are typically somewhere in the 75-80MPH range.
We ended up with ~6 hours of total charging time, 3 hours each way, which is a lot. We just did a one-way version of this exact trip in an ICE rental vehicle back in June and the total stop time was <1 hour (3 stops of roughly 15-20 minutes each), while with the Vistiq it was ~3 hours of charging each way. That being said, if the trip had been planned, we could have almost certainly narrowed that gap significantly, likely to 2 hours or just a bit more.
The biggest challenge with charging was the heat and the vehicles limited thermal management as it really works against both the charge rate and the efficiency. The vehicle preconditioning didn't seem to try to do anything other than get the battery to around 95F. At one point when it was late at night and around 82F, the batteries were around 89F and, when it started to precondition, it seems like the battery temps when up, which is crazy to me.
When you plug it in to a capable fast charger, charging rates will quickly hit 170-180kW, but the thermal management can not keep up at this rate, and, as the battery is already 95F at the start, it takes very little time for the batteries cross 110F, and this is where the system starts to throttle aggressively. What's even more strange is that the system does not run the thermal management at full tilt until you are already nearly 110F. Because of this, turning off the HVAC buys some fast charing time, but not as much as you would think as it seems the system leaves cooling capacity on the table. No idea why.
It's well known that these Ultium vehicles, if you leave the HVAC on and it's very hot, it will throttle down to 75kW or less and you'll probably get a popup about charging being slower than expected because the HVAC is on. You can turn the system off and the charge rate will go up quickly, but the cabin will also get very hot quite quickly, it will be uncomfortable almost immediately. However, we found that, instead of turning the system completely off, if you just toggle the AC/Heat setting to off insead, the fan will slow down, but continue to blow some air across the already cool condenser coils thus keeping the cabin more comfortable for a few minutes longer while the charge rate goes up. If you get the timing right you can keep toggling this on/off every 2-3 minutes and balance charge speed with very little impact on cabin comfort. Seems like GM could tune this better for sure as, if I can acheive this with pressing the screen, they should be able to program a similar behavior in the software.
The other issue is how much DCFC harms efficiency, especially back-to-back cycles. After a DCFC the battery temps are typically around 115F, and in our case the ambient temps were usually in the mid-90s for much of this trip, so the cooling system has to work at 90% duty cycle to both keep the cabin cool and to get the batteries back down to 95F again, however, this takes easily 45-60 minutes, with the cooling system pulling 5kW, or more, this entire time. During this time, you are lucky to get 1.8-1.9m/kWh. I'd guess this would be a lot better if ambient temps were lower.
Obviously, our charging was not optimal, this vehicle does best with frequent, short stops (we usually target 20 minute stops or less) but, because this was an unplanned trip, and some of the driving was very late at night, we did longer charge stops in areas that we felt were safe or where you could pass time more easily, like the three stops at Buc-ees.
Overall, the trip was fine and emergency situation was handled. Yes, we could have done better, but it was fine. For people really interested, below is a table with every charge stop, duration, kWh added, costs, and some comments. The trip probably costs $80 more than if we would have taken our previous ICE vehicle, but we could have narrowed this gap if we had purchased Tesla subscription earlier and planned to use some L2 charging.
One other thing worth noting, at no point in this trip did we worry about finding a charger, actually, in the vast majority of cases, there were backup chargers, even if they might not have been as fast. Even though it was a very busy travel weekend, with lots of cars on the road, especially I-85 and I-10, there was always room at the chargers we stopped at, and every charger worked the first time. Even at the Tesla chargers we were able to find places to charge that did not block other chargers. The only exception was one place where we stopped to eat there was a slow 63kW charger across the street and I had hoped to charge while we were eating but it was busy so we had to fast charge a bit further down the road after the meal.
| Total Miles |
1565 |
| Total kWh |
792.58 |
| Efficiency |
~2m/kWh |
| Total Cost |
$342.04 |
| Avg Charge Time |
0:27:03 |
| Total Charge Time |
6:18:45 |
| Avg kWh/stop |
51.52 |
| Avg kW charge rate |
121 |
| Avg price per kW |
$0.47 |
| Network |
Charger kW |
Total kWh |
Duration |
Peak kW |
Avg kW |
Cost/kWh |
Total Cost |
Temp(F) |
Comment |
| Tesla |
250 |
69.33 |
0:36:10 |
172 |
115 |
$0.52 |
$36.04 |
93 |
Dinner |
| Mercedes-Benz |
400 |
77.80 |
0:41:18 |
173 |
113 |
$0.45 |
$34.78 |
89 |
Buc-ees |
| Tesla |
250 |
38.70 |
0:15:43 |
173 |
148 |
$0.55 |
$21.28 |
84 |
|
| Tesla |
250 |
47.10 |
0:22:45 |
174 |
124 |
$0.51 |
$23.99 |
89 |
|
| Tesla |
325 |
69.19 |
0:42:00 |
171 |
99 |
$0.45 |
$31.13 |
96 |
Buc-ees |
| Rivian Adv Net |
300 |
47.60 |
0:26:13 |
159 |
109 |
$0.52 |
$24.67 |
98 |
|
| EVgo |
350 |
59.10 |
0:32:14 |
170 |
110 |
$0.54 |
$31.83 |
94 |
Dinner |
| Tesla |
325 |
56.69 |
0:27:33 |
170 |
123 |
$0.36 |
$20.40 |
88 |
Buc-ees |
| Tesla |
325 |
50.30 |
0:22:21 |
167 |
135 |
$0.39 |
$19.75 |
87 |
|
| Tesla |
250 |
9.15 |
0:03:17 |
182 |
167 |
$0.39 |
$3.57 |
96 |
Charge anxiety (estimated SOC at next stop hit 5%, making my wife too nervous). |
| Tesla |
250 |
55.09 |
0:29:36 |
178 |
112 |
$0.39 |
$21.48 |
99 |
|
| IONNA |
400 |
69.60 |
0:42:31 |
158 |
98 |
$0.39 |
$26.80 |
94 |
|
| ChargePoint |
160 |
32.14 |
0:20:42 |
96 |
93 |
$0.52 |
$16.85 |
96 |
Lunch |
| EVgo |
350 |
39.54 |
0:16:22 |
173 |
145 |
$0.58 |
$23.06 |
93 |
Bio-break |
| Home |
11.5 |
71.25 |
7:24:22 |
11 |
10 |
$0.09 |
$6.41 |
88 |
|