Hi @kai_ ,
Not implying anything but.... ;-)
Have you verified that the batteries are installed correctly and that the camera's battery terminals are bright and shiny and that there is enough tension being exerted onto the batteries to ensure that there is a good connection?
Here's a link to the User Manual, scroll to p.9 to view battery installation and type information
Hi @kai_ ,
Actually the 357/303 are silver oxide batteries and are reputed to last up to 4 x longer than the LR44 which are alkaline.
I don't know your camera but am just verifying that you installed the batteries correctly in "series" connection, That is +ve side of 1st battery up into the battery cap then +ve side of 2nd battery up, therefore +ve side of 2nd battery connects to camera terminal and -ve side connects to internal cap end (which should have a metal contact plate) when batteries inserted and cap locked down giving 3V battery. (See green arrow in image)
There is a battery installation picture in the battery cap which may show it better than I have explained, (shown by the red arrow in the image).
(click on image to enlarge for better viewing)