Over the weekend shooting an event, I placed a fully charged battery in my camera and I get the 'can't communicate with battery' message. I tried placing another battery in and I get the same message. These batteries show fine on the 60D, so it is just the 7D that has this problem.

Has anyone had this happen to them? I'm out of warranty now, so a DIY fix would be great!

I had that problem not too long ago. I had a canon battery grip attached and a oem bat and an opteka bat in it. Removed the grip and just used the oem bat and have had no problems as of yet. Are you using oem batteries or off brand batteries?

I use a mix of oem and off brand batteries that can communicate with the camera.
In the end, I took it to Canon and they changed the board I think. Costed $80 and done in 2 days.

Ps, I'm only using Oem batts now