At least in theory the battery could be used to recover some of the energy on descent (similar to regenerative braking, but with the spinning propeller instead of wheels). No idea if that’s at all efficient or if anyone experimented with this though.
The main drawback to that suggestion is that aircraft really don't need more charge as they descend.
The high-energy flight segments are take-off and climb. If you're charging batteries on descent ... the only gain is that the next take-off/climb phase can use that recovered energy.
But from a mass and capacity standpoint, which seem to be the real challenges for electric flight, you're gaining very little. The ability to get rid of the battery you've spent on take-off/climb would be far more useful.
