Why is my battery light on?
The battery light doesn't mean 'replace your battery' — it means the charging system isn't keeping the battery topped up. Almost always: a failed alternator, a broken/loose serpentine belt, or a bad voltage regulator. With the engine running, a healthy system reads 13.8–14.4V at the battery; under 13V means you're running on stored battery only and have minutes to hours before the car dies completely.
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