Disconnecting the battery while the engine is running isn't a valid test for alternator function and may damage sensitive electronic parts. Instead, use a common voltmeter and the following test ...

The alternator is responsible for charging the car battery and powering all the car's onboard network consumers. If it fails or is unstable, the battery will either not be charged or start discharging ...

The alternator in my daily driver 2003 BMW 530i just died. Before I delve into the nuts and bolts of the replacement, it’ll be useful to give you the context on alternators in daily driven modern cars ...