Two days prior to a photography trip to Yellowstone while charging and checking my batteries, I received the error “Cannot Communicate to Battery” while inserted a freshly charged battery in my Canon 7d. The camera still appeared to have power. However, the battery indicator showed that the battery was empty and I received the error each and every time I turned the camera on.
After scouring the Internet and finding limited information, I thought I’d pass along how I fixed the problem.
The fix was simple. Remove both the LP-E6 battery and the clock battery for around 20 minutes. The clock battery is located inside the main battery compartment right next to the hinge for the compartment door. When you reinstall both batteries, the problem should go away. I received the error one additional time after reinserting the batteries. But, once I set the date and time, and turned the camera on and off the problem went away.
If this doesn't work, you may have to send the camera off to be repaired. The functioned correctly to take photographs. It only lost the date and time and got an error each time a new battery was inserted.
But before you send your camera off for repair, try this quick and easy fix first.