I know with usps, it doesnt matter what level you ship them at, 1st class or priority, they all get sent ground. Fedex may have different standards in terms of how big a lithium batter has to be bedore it goes ground only, and sometimes it makes a difference if the battery is by itself/tool battery, versus it already being inside an electronic item, like a fitbit. The size of the battery changes how they ship and whether or not its a standalone battery versus being inside something, makes a difference.
I looked up what I needed to do and did it. It was a set of cordless tools with several batteries.
They didn’t seem to care. So I didn’t worry as much for the return delivery.