DJI themselves spec the battery as good for 300 charging cycles. Based on my current number of cycles and % of life reported by the battery via the Assistant that is both realistic and a little conservative (I don't push my batteries hard, though - always land before they drop below 18%).
Assuming an average of 22 mins flight per discharge cycle that works out at about £1 per hour of actual flying time as an ongoing "consumable" expense... Obviously that's +/- but doesn't seem outrageous to me (especially as a two-battery sortie, with travelling and setup time keeps me out of the house for about an hour and a half). Actually - capital cost of aircraft aside - that seems **** cheap for something I enjoy rather a lot! I would get my wife, who's an accountant, to amortize the capital cost into the expected lifespan of the whole unit plus depreciation and factor in some extra for spare motors, etc, to get a true hourly cost but I'd actually quite like to keep my genitalia intact a bit longer.
and once done turn over the keys and go on to the next game changer 
