MT Shooter wrote:
Sounds VERY much like a battery issue. OEM, generic, counterfeit? Fully charged both before shoot? Selected battery order? (Grip or body first?) I seriously doubt its a camera issue and would bet its a battery issue for sure.
I agree that the battery is the most likely cause of the issue. After a significant number of charge/discharge cycles (either partial or full) the internal resistance in batteries increases so that even a fully charged battery will supply less peak current to drive the motors and electronics than would a new battery.