New save battery, lost only one of my two saves Sim City cities

I was super happy to have a new fresh working battery in my copy of Sim City.

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I made a test save after I put in the new battery and then I had a rather epic city going on the other save file for days.

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Then I wake up this morning and only the test city is there. It's not as if both save files got erased, just the one I care about.

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Is there anything I can do to get it back?

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Should I remove and resolder the battery?

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Is this the saddest day of my life?