I have a new proposition for the electric categories we are about to establish in Greece. The goal is to fly for 30 minutes. Any motor, any battery, any model. Those that land before the 30 min get their position respectively. The round ends at the 30 min. mark. Those that are still airborne, may land, no extra time counts. Their classification is calculated by a weight factor : i.e. divide battery weight by the airframe weight. The best weight factor (lighter battery in respect to heavier model) goes on top. This forces the pilots to choose the lightest battery for their model, that is needed to fly for 30 minutes, depending of course on the model's performance, their flying skill and the day's thermal activity (if they can't have a lighter battery, they may add ballast to the model to get a better factor).

The picture is of my model ME109 with a 46 inch span foam wing. It uses a WLM wet mag motor and 8x4 slim prop. I use 7  Nickel Metal Hydride 2200 mAh cells to get 7 minutes of full throttle.  I recently changed the spinner for a section of a white expanded polystyrene egg that I found in a local hobby store.  It is much lighter and saves any balance problems.
I recharge the NiMH using a standard delta peak charger at 3.4 A. Discharge whilst flying is about 19 A to get 7 mins flying time. Depends how continue