Most people understand that their car needs a battery in order to get going each morning. Yet some people believe that this device is responsible for operating a range of different electrical components, once the car is underway. Unfortunately, the battery is not powerful enough to do this and needs a generator to make everything work correctly. This alternator will, nevertheless, recharge the battery under normal operating conditions. So, if you clearly have an electrical problem, how can you tell if it is the alternator or the battery?
Before you open the bonnet and start poking around, sit in your car and try to crank the ignition. As you turn the key to the first position, the dials and lights on your dashboard should activate. If they come on and the various lamps appear to be bright, then your battery should be okay. If you have a separate voltmeter amid your instrument cluster and have a strong reading, your battery is good.
When you turn the key further and attempt to crank the car, the starter motor should spin actively. This signifies that the battery has enough charge to perform its primary task.
You may get some early warning signs when driving in the dark. For example, you may notice that the headlights seem to glow brighter when you place your foot on the throttle and become dim when you remove the power. Some of the warning lights on your dashboard may also flicker in this situation, and this signifies that outward from the alternator is varied. Once the voltage drops below a critical level, a sensor will send a signal to the ECU, and this should activate a warning light on your dashboard.
If the alternator has been playing up for some time, then don't be surprised if the battery appears to be dead one morning. In this case, the alternator has been unable to charge it, and all the other ancillary electrical parts have drained what is left of the power.
In this situation, you can find out whether it's the alternator or the battery by jumpstarting the vehicle and then removing the cables. If the alternator is in good health, then the engine should continue to run, but if not, it will quickly splutter to a halt.
Time for an Electrician
If you're still confused and cannot tell whether it's your battery or alternator, turn everything over to an auto electrics service. They will run a variety of tests and get to the bottom of the issue for you.