Easy way to check with a voltmeter. Check battery voltage on the battery terminals with key off, engine off, and then check voltage with engine running.
Engine off, a good battery should have voltage between 12.6 volts and 12.9 volts. With engine running, battery voltage should be a minimum of 13.5 volts, somewhere between 13.5 and 14.5 volts. This would indicate the alternator is good and is charging the battery. If voltage is less than 13.5 volts, if it only shows same volts as when not running, the alternator is not working right. Take it off and have tested for free at a parts store. It could be a bad alternator or it could be that the wiring between alternator and battery has a problem. If alternator tests good, start looking into the connections between alternator and battery.
Does your battery or alternator light stay on when engine is running? This would indicate a charging system problem. Time for the voltmeter test.
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