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Question: t-10 olympus forget the time after every power off

I have a T-10 Olimpus about 2 years , and i am wery satisfaid about this camera.
from a time ,every time when I start (power on) my camera he ask me for time set : hour, date, etc. I want to ask if somebody know if there is an extra battery hwo keep the time and how i can change that. Thanks a lot.