Battery depletion message - unable to use cameras

Using a SanDisk Ultra II 6 GB card in a Pentax Optio. I've used many of these before with no problem. This time the camera battery kept depleting -- new batteries - same message. I felt it was a camera problem - not thinking it could be a disk problem. Because I have a wonderful photo of a Pearl Harbor Veteran who died this past week, I once again tried to get the photos downloaded to my computer. They are there - I can see them on the review - but cannot get power to download them. I put the disk in my Panasonic Lumix to see if I could load the photos from it -- and darn - the same battery depleted message appeared. When I returned the good SanDisk card to the Panasonic, it appears now that camera has battery depletion messages. I am charging the battery -- and will see what happens.

Is there anything I can do - I do not want to lose the use of both my cameras. And I want the photo of this wonderful veteran.

Veteran friend in WA