EF 70-200 f2.8 II Stops Focusing after a few hours of shooting

[kalw63]

I bought a used EF 70-200 f2.8 II from KEH a couple of years ago. It was rated as EX (excellent) by KEH. It usually works perfectly for casual shooting or covering short events/sessions, but when I shoot sporting events, it loses the ability to focus after a few hours. I'm shooting outside typically in pretty warm weather (80 degrees F / 26 degrees C), and I'm not sure if that may have something to do with it.

I use a 7D mk II body with the lens, and am shooting roughly 2,000 frames per day; the problem begins after about 1,000 frames. I use back button focus.

Has anyone else ever had this or a similar problem, and if so, how did you solve it?

[Waddizzle]

Are you using any custom shooting modes?

[Waddizzle]

Also, a low battery slows frame rates and AF speeds, but not stop working. 

[ebiggs1]

The only thing you can do is reset the camera to default to make sure it isn't a setting. Try it. However, the lens is probably faulty and needs service. KEH doesn't do anything except look at a lens and give it a rating. Oh sure, they may stick it on a camera to make sure it works but that's it.