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A warm welcome to the Community @Lucy58. Your Zip's battery should last 6 months. If the battery you placed is not that old, sometimes the side spring may be bent as a result of improper battery insertion or pressure being applied to the back housing.
Please verify that there is proper contact between the battery and the battery contacts inside your Zip tracker. You can do this by opening the battery door of your Zip, removing your battery, and ensuring that the silver battery tab located in the lower right half of your tracker is flush with the white box outline in the tracker housing. The process can be followed here.
Let me know the outcome. 
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