- 1). Look at the voltmeter on the dashboard of your vehicle. Cars operate on a 12-volt electrical system. A fully charged battery should read about 12.5 volts when the key is in the ignition and turned partially, but the car's engine is not running.
- 2). Look at the voltmeter while the engine is running. Readings of 14 to 14.5 volts on the gauge when as a good sign. This is typical of a properly operating charging system. If the voltage reading drops below 12.5 volts, the charging system is not operating properly, and the battery is having to provide current, meaning it will eventually go dead.
- 3). Find the ammeter on the dashboard. The ammeter gauge should read a little greater than zero when the engine is on and the system is functioning properly. This means that the battery is fully charged and the charging system is providing the current. A negative reading (below zero) means the battery is providing current, and unless the problem is corrected, the battery will go dead.
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