So my memory is not the greatest, and something that was a major inconvenience during a road trip might have given some valuable data. On a 50 kW charger, it appears that the Bolt EV can recharge from 35% SOC to 69% SOC (roughly 35% capacity) in exactly 30 minutes. Assuming the Bolt EV can charge at a faster rate below 40% SOC than above, this might provide some valuable data about the actual charge rates. I still don't have access to any chargers operating at faster than 50 kW, so we will have to wait and see what the actual fastest charge rates for the Bolt EV are.
You charged at a rate of ~162 EPA miles range per hour. At least one other has demonstrated just over 180 mi range per hour rate, also on a 125A charger.
Calling a charger "50kW" is somewhat meaningless when you're interested in describing the maximum charge rate of the unit. This is because the charger manufacturers don't use a common way to describe their power output. I understand there are at least 3 different kinds of "50kW" class DC fast chargers.
1) 100A @ 500V = 50kW
2) 125A @ 400V = 50kW
3) 125A @ 500V = 62.5kW
But realize that the maximum charge power (eg charge rate) occurs when the charging voltage is at just under 400V and at the maximum current capability of the charger. Let's assume the charging voltage is 390V for the following calculations. Here is the maximum power expected from these chargers:
1) 100A @ 390V = 39.0kW
2) 125A @ 390V = 48.8kW
3) 125A @ 390V = 48.8kW
Here you can see that the charge current, in amps, is actually the most relevant number to know when charging today's EVs with ~400V batteries.
But how do we know the amperage of the charger? Besides looking on the back of the charging unit and looking at the spec plate, the best way to know is if you car is actually charging at more than 40kW. If it is, then you know you're at a 125A charger. Unfortunately PlugShare and similar sites/apps don't make ANY reference to charger power so you may be reliant on looking at their pictures of the site and recognizing specific charger models.
A typical Li-ion charging cycle consists of 2 phases, a constant current (CC) phase first and a constant voltage (CV) phase last. When a battery is charged from empty a constant current is used. As the battery charge increases the voltage rises until the cells reach maximum desired voltage and the charger then holds constant voltage but lets the current drop. The CV phase is when tapering occurs as it's when the charging power is decreasing towards the end of the charge cycle.
Recall that power (kW) is volts (V) times amps (A), so the maximum power and charging rate occurs when the current is highest and the voltage is highest. This occurs just before tapering begins at the transition from CC to CV phases. So charge rate is actually INCREASING until tapering begins.
Today's 400V BEV batteries that can charge at 125A and are on a 125A charger, will start the charge cycle at maybe 330V and will charge at ~41kW [330x125] under optimal conditions. It's not until the battery reaches max voltage that the peak power is produced, and then it's only an instaneous peak as the charger transitions from CC to CV. As shown above, that peak could be ~49kW for today's BEVs on a 125A charger and capable of charging at 125A.
I've tried to describe optimal and generic charging. There are a multitude of factors that result in lower charging performance.