In a Bahrain quali lap, Maximum ERS Boost only engaged for about 7 seconds.
Because the full ERS boost sound (wastegate fully open, turbine driven only by MGU-H, the same as the Overtake Mode) is very distinguishable on Alpha Tauri's exhaust mic, it is possible to draw on the map the sections where the full boost is engaged. Bahrain is known for the long straights, so it's only 7s affordable and they use it where it matters the most, to maximize the corner exit speed at T1, 10 & 13. Each is around 2s and each consumes about 8-9% of the battery which is pretty intense.