My xbox360 clock keeps resetting.?

I'm playing Castle Wolfenstein, and when I stop and start – keeps kicking back to a previous game. I it was a mistake, but then I realized that my Xbox keeps clock reset to 1995. The game incorporates the latest save / last in time. Is there a battery needs replacing or something to make the clock keep better time? I do not live that does not sync with Live. The box stays connected all the time.

There is a backup battery, but you can not change it. However, it is only used when the Xbox 360 power supply is disconnected from the wall wall.

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