One would have to calculate that. The FP also uses a rechargeable battery. But probably it’s more efficient to not use Li-Ion batteries.
What about an induction approach? At least you move your mouse all the time, so it could generate energy through the movement.
Back to the topic: I just have a problem with the wire because it’s one part of a mouse which breaks easily.
PS: I can’t reply through a new thread on the Fairphone… Maybe we could/should discuss this in a new thread?