Originally posted by Ash Could it possibly be battery power? I tried with 2 fully charged batteries (1 in body, 1 in grip) and still same result...
I had one battery, original KM HP-400, that even fully charged, would die prematurely.
I'm not sure how the battery grip works with the battery in the camera, but it might be possible that one bad battery would effect the operation of the other good one. I would test single batteries without using the grip to see if you can isolate the issue to one or more batteries.
If you can't isolate the issue to a battery, I would try to determine how may shots a battery could take using a higher, above 1/4 second, shutter speed. If the issue appears to only be seen in bulb mode, then it is likely a camera issue.
I would also look at using another charger if the issue isn't just related to long exposures and appears across multiple single batteries.
Thank you
Russell