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any auto parts store

cant test both of those for free

You can also test them yourself if you have a digital multi-meter. The battery will read 12.6 volts when fully charged. 12.4 at 75% charge, 12.2 at 50% charge, and 12.0 at 25% charge. With the engine at idle you should read from 13.5 to 15.5 volts at the battery if the alternator is good.

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Q: How do you tell if the alternator or the battery is bad?
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