Miles To E Reading Wrong

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My cd player was reading "disc error", and when this happened in my Lincoln a simple undoing of the battery fixed the trick so I tried this with my Milan. After doing so, I noticed that my "miles to e" tracker was way off; it added about 30 extra miles. I would fill; my tank and it would always read around 260 miles to e. Now it read over 300 sometimes. When it gets down to 50, a sound is made; this used to happen at a little under a quarter of a tank. Now it happens when the gauge is next to E!!! The needle will be on top of the line marked E and it will tell me I have 30 miles to E. The battery was disconnected once more at a later date, and it had reset when I tured the car on, reading 253 miles to e, then I drove for about 5 miles and it reset to 311. How can I fix this??