if a measurement like time remaining can change at random based on load and the load can change at random based on user behavior then why show time remaining at all?
if it jumps from 90 minutes to 10 minutes, what's the point of even showing it?
"okay now i have 10 minutes left"
it would be more accurate to say "you have 90 minutes left at your current level of cpu utilization" but i don't think that can fit in the menu
help me figure it out, i don't get why a user would need this functionality ever.
If user have forgotten that, it's no reason to remove it.
In fact there's rarely a reason to remove a feature if it doesn't cause issues.
Taking your own exemple of video rendering, if I begin a render and After Effect (or similar) says it will take 50 minutes to render, but the remaining time says I only have 20 minutes left of battery (implying "at the current load"), I know I have to charge my laptop if I want to render the video.
It evaluates the remaining time using current ressource usage. It is "accurate". It can't predict how much time your rendering will take, it can't predict the future. But it does an accurate estimate of how much the battery will last under the current load.
(imo, current load is better than trying to compute the load trend)