Apparently as often as you loose drones, 1 back up is insufficient. You probably need 3 or 4. Possibly you could get a discount on Amazon with a subscription and autoship once very few months. I do that with my boat supplies.
I am at 380' ASL. I only have 20' above home point if I head over the ocean. You can see the helicopters far below my 400'. Always on the lookout, they do this frequently.