I know so many people going through the same thing with their kids at just about the same age. From what I have seen, ALL their kids choose "electronics" over being outside and that is where the problem gets started in the first place. They catch the electronics bug and nothing else seems as fun to them and believe me, I'd heard the very best whiners and complainers when it comes to not wanting to do this or that outside....they don't like it, they're bored, they're too tired or it's too hot. I've heard it ALL.
I only have one friend who made the plunge and took the electronics and video games away all together. No more arguing about being outside with the rest of the family. When the weather is bad, they play cards or board games so that everyone is engaged.
Kids need to be active. It's good for them whether they believe it or not. My one friend's son has become seriously overweight and all he wants to do is sit in front of a TV video game. She lets him because it's easier than listening to him gripe. He doesn't even want to leave the house to go camping or to car races or anything that most boys would like. He just wants to sit. What he WANTS and what is best are two different things.
I would remove all electronics. Not as a punishment, but as something to be earned.
For every hour he rides a bike with you or does something else like shoot baskets, he earns 15 minutes. He adds up his time during the week and gets to cash in on the weekend (or whatever day you choose). 5 hours during the week earns 1 hour and 15 minutes, and so on. He can take it or leave it. He's still going to do the activity, and if he doesn't think the time share is fair, fine....zero electronics then. I think you'll find that in the end he will have more fun getting out and doing things and the electronics will fade out a bit. Either that....or he'll be dragging YOU out for activities to earn his electronic time.
Don't just let him sit in the house all day. Even the most cerebral of individuals need to get out and get fresh air and exercise. It makes for healthy children, to be sure.
Best wishes.