Because timezones were a result of town specific clocks, which were a result of people liking certain hours happening generally in line with where the sun is, like "noon" which still technically refers to when the sun is at its highest point.
Also, that 40% figure is not a battery percentage, nor is it a percentage of battery usage from full charge, its the worst possible statistic that could have been used: a percentage of battery usage where "100%" is the total recorded battery usage of all things in the category you're viewing.
And no that isn't clear or well documented in any way.
Because timezones were a result of town specific clocks, which were a result of people liking certain hours happening generally in line with where the sun is, like "noon" which still technically refers to when the sun is at its highest point.