Has your vehicle's alternator failed? Are you absolutely certain that it isn't your battery or starter? Determining which part has failed is essential toward avoiding unnecessarily replacing something that hasn't failed, like your battery. Let's take a look at some steps you can take to determine that your alternator, in fact, has bit the dust. If you own an alternator testing machine, you can test to see whether your car's alternator is charging correctly. For most people this isn't practical as few motorists own such an expensive piece of equipment. For everyone else, there is a practical way for you to easily check to see if your alternator is working properly: