From Canon USA
Canon continues to update older professional DSLR bodies. I must say I'm pleasantly surprised they're still supporting the Mark III bodies.
The following fixes have been incorporated in the new firmware
- Resolves the following phenomenon: when the camera is not attached to a lens, power consumption may be higher than usual, causing premature battery drain.
- Resolves a phenomenon in which “Err 02” may be displayed when the shutter is released without a lens attached.
Download the firmware