Q: I don't know whether it is the alternator or battery

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Yesterday my car was driving fine and this morning I went to start it up and the battery was dead but the lights came on . I don't know if it is The battery or alternator
My car has an automatic transmission.

The best way to determine if your alternator or battery has failed is to start with a fully charged battery. I would recommend having your battery fully charged. If the battery will not accept a charge, the battery has likely failed. If the battery does accept a full charge, reinstall the battery in the vehicle and start it up. Then use a digital multimeter to check the charge output of the alternator. If the alternator is not producing at least 14 volts, the alternator has failed. If you are in doubt about any of these tests, consider YourMechanic as a certified professional can inspect your vehicle at your home or office.

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