We may occasionally write gallons per mile with a slash, but it is useful as a ratio, not an equation. It makes no sense to reduce a volume to a surface.
On the other hand, knowing if a factory puts out 240 gigawatt hours worth of battery capacity every year, or only over the entire lifetime of the factory, really is an important distinction to make.
Sure, but to be useful you need flow rate, at which point you're basically back to calculating volume. Gas is purchased in volume, and stored in volume. Why not keep the measurement of use as volume per time or distance?
I wish people like you who make these intelligent,factual, and short comments could have a reputation value on HN. This value could give you some automatic upvotes or a more prominent location displayed.
On the other hand, knowing if a factory puts out 240 gigawatt hours worth of battery capacity every year, or only over the entire lifetime of the factory, really is an important distinction to make.