I have a voltmeter and an ammeter. Both are valuable. The voltmeter hangs below in an aftermarket bracket. The voltmeter will tell you the health of the battery before starting the car and the health of the generator/alternator when driving. If you have a generator you can better tell is it set too high or too low. The ammeter will tell you when the battery is being charged or discharged or if the points are operating as they should. If the generator or alternator fail the voltmeter will tell you how much juice you have left to make it to home or to a convenient place to stop.