Most Canon cameras have a small rechargable battery for the date/time.
Since your camera is new and under warranty, I suggest you contact Canon Service about this problem.
...
..
.
having only recently bought my powershot A620, i have been reading up on the functions. On one page it states that a small rechargable battery charges up from the main batteries to keep the date and time stored in the camera. however whenever i take out my batteries i have to reset the date/ time. Has anyone else encountered this problem and have you managed to solve it.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic