As I’ve documented on a flight with my 2020 iPad Pro (A12x = M1 predecessor), my accumulated sessions might’ve totaled at least 5 hours (accounting for additional usage time at the gate). As the cabin was overall dim, I didn’t need to crank my brightness at all. That likely helped the tablet conserve battery power.
With the upcoming M3 iPad Pro, it’ll be entertaining to see whether the chip’s 3nanometer manufacturing process will help its efficiency… whatever the case, it’ll be offset against the thinner 5.6mm to 5.0mm redesign (likely less battery capacity) and might be affected by the change-over to a double-stacked OLED setup. In a general OLED vs LCD query, some are suggesting OLED tends to be more power-efficient, but in the new iPad’s situation, there’s TWO stacked OLED screens for bringing brightness closer to what LCD/microLED can achieve.