Here is what I did to unlock this:
Grand Prix > Mercedes
Select Canada as the track.
In Race Settings go for 5 laps, then Rules & Flags off.
Once you begin the race, turn ERS up to  and Fuel up to .
Drive the majority of the, Lap normally but when you get to the final straight cut the chicane entirely while going full-throttle. If you let off the throttle at any point the battery will begin to recharge.
You should be near 0% already after 2-3 laps but I’ve set it to 5 so you have some buffer room to fully deplete the battery. Just make sure to cut that final chicane every lap and you’ll unlock this at the end of the race.