Battery levels

[jpj. 92]

Hi all, clocked a 28km off road ride today with 800 m of climbing, kept a check on my battery as didn't want to get caught short.. St unlocker app showed 31 percent remaining shortly after I dropped to one red bar (I'm guessing it does this at 35 percent then?) just curious as to when it dies what percentage it shuts down on as last time I got to red I had little warning before it then shut down?