A better incentive would be to give chargers a tiny cut of all the riding fees for the next charge. Make it so the scooter have to be below 50% battery OR not ridden for a day in order to be eligible to move. That would incentivize the chargers to get the scooters back on the street ASAP.

If there’s still hoarding, offer riders (not chargers!) some bounty for reporting hoarding.

As other posters have said it’s a game-design problem to align incentives so that you get the outcomes you want.