I replaced the battery when my car’s battery light came on but it did not fix the problem. What else could be causing the light to come on?

The alternator may not be recharging the battery. To complete a simple test on the alternator, follow these steps. Obtain a voltmeter that can test direct current (DC) voltage. Connect the voltmeter to the battery. With the engine off, the reading should be around 12.1 to 12.6 volts. Start the engine. The voltmeter now should show a reading of 13.6 to 14.6 volts. If the reading is less than that, the alternator may not be recharging the battery as required.