We all know that capacity of alkaline batteries is lower if the current is higher. What puzzles me is the effect of PWM on batteries.
Let’s say I have a 500mA driver with a 20% duty cycle. What discharge time to expect? The 500mA x5 or the 100mA? Any idea?
I think somewhere in between, but closer 100mA. I don’t think PWM is 100% efficient with batteries, but on low modes, you should still see significantly longer runtime than high.
Most analyzing chargers uses pwm, that do not affect their result much.
Yep, my flashlights all run longer on low than on high. 
Just guessing, but the battery is a chemical process where something is converted to something else creating some electricity and some heat. Under high drain over time heat builds up that reduces efficiency and the chemical reaction may have “flow” issues which ultimately set the max drain rate. PWM is a higher drain, then off , then drain, where average drain may be the only real factor as the average drain is the build up.