When i turn it on again it still asks for the date and time

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Where can i find thet inyernal battery and how i replace it.

As i turn it on i have To enter the date. When i tu en it on avait it atilo sais for thé date.

Where van i fond thé infernal batyery or canon s110 and how i replace it.

Tjanx.

Because as i enter thé date when i close ou and tu en or on avait ou asks me To enter thé date.