Range isn't a unit though, so it isn't actually telling you anything technical. Since range is a distance unit, it would still be "miles per hour" or "kilometers per hour" or "meters per second" or anything to let you know how long it will take to top up to full range.

Could be "%/minute" maybe, but that is less useful if you know you need to go 45 miles, you would want to know how many hours (or fraction there of) that would take.