I lost my battery door months ago after misplacing it and upgrading to an external battery pack grip. The camera (Canon 5D) one day mysteriously stopped working and I assumed the battery pack was kaput. Although the LCD moniter on the battery pack is fully functional, it cannot seem to supply power to the camera. All the batteries work and are fully charged, but when putting them into the camera (not the battery grip) the camera cannot turn on.
Should the camera be unable to turn on without a camera battery door, or is something more sinister wrong with my camera? Ultimately I want to know if I should buy a battery door? Is there any way of testing if I need one before committing to buy one?
There's a little switch that is triggered by the battery door and grips that allow the camera to power on. When that switch isn't triggered by either a battery door or the grip it won't power on. Getting a replacement door is your best option, since it will properly protect your body, battery and trigger the switch, but in the meantime, you can rig something up to push the switch in and allow you to use the camera.
It's possible that the little tooth on the grip that triggers the switch on the body broke off and that's why the body isn't powering on.