Your car’s battery can only go so far by itself. The alternator keeps it charged and powers all your car’s accessories by converting your engine’s mechanical energy into electricity. Regular use wears hard on it, especially with more devices and complex systems. Most drivers have plenty of warning before their alternators fail, however. A warning light labeled “ALT” or “GEN” indicates alternator problems, but other telltale signs include dim lights, a whining noise or a burning rubber smell. Also, the battery may die sooner than it should. You can use a voltmeter to test alternators, and with the right tools and the vehicle's service manual, you can even replace them yourself.