Leave it in his jeans while doing the laundry and let the spin charge it?
That's along the lines of what I was thinking. Though, the water might delete the magic of them. Maybe ride a bike with the rings somehow attached to wheels.
Maybe this thread becomes a list of top ten ways to recharge Harry's rings!
10. Spin cycle of the wahing machine (with possible issues)
9. Bicycle ride with rings attached to wheels
8. Mouse dries himself after a bath (Rotational velocity)
7.
Okay Folks! Add yours to the list!