How to tell if battery is bad or alternator?

Hello guys, I was working out of town when my truck’s battery died. After getting a jumpstart, I drove back to the hotel, but the battery died again as soon as I turned off the engine. How can I determine whether the battery or alternator is the problem? I would like to avoid purchasing a new battery only to discover that the issue lies with the alternator.

Hey Ben,An effective method to determine whether it’s your battery or alternator that’s gone bad is to connect jumper cables from a running vehicle’s battery to yours . After a few moments, try starting your vehicle. Once it’s started, remove the jumper cables — if your engine stalls, your alternator has probably gone bad

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When the alternator goes bad and stops charging the battery, you’ll typically notice the red “battery” warning light illuminating while the engine is running. If the warning light didn’t come on while the engine was running, it’s likely that the alternator is fine. Based on my experience, if the alternator did come on, it’s likely that it’s faulty.

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To determine if a battery or alternator is bad, use a voltmeter to check battery voltage when the car is off (should be around 12.6V) and running (should be 13.7-14.7V).