About Car Batteries

By Mark Gittelman in Auto Repair Information

Information about Car Batteries

I have written a lot of articles about car batteries and charging systems. One question has come up frequently that seems to have fallen through the cracks of the articles that I have already written about the battery and charging system on modern-day cars.

This frequently asked question about the vehicle’s car battery is after the engine is running is the battery doing anything besides charging back up. The short answer to this question is no. The battery is used primarily for starting the engine.

In fact during cranking it is the battery that supplies all of the vehicles electrical power. However, once the engine is running it is the alternator that is responsible for producing enough electrical energy to meet the demands of all of the vehicles loads. This would include things like operating the wipers illuminating the headlights and even charging your cell phone.

After all of the current demands have been met any excessive electrical power available is used to recharge the vehicle’s battery. This is one of the more important details about car batteries. With the increase demand of vehicles optional accessories for some motorists the excessive electrical current used for charging the battery may be in short supply.

This is also why that the vehicle run time between engine starts is also so important. If only a small amount of excess electrical current is being funneled to the battery then a longer run-time might be required to fully charge the battery for the next starting cycle. I have written a complete article on this subject that discusses how long a car battery will last.

Monitoring the Car Battery

Another question I get about car batteries is what to do when a warning light comes on in the dash panel. Most often these warning lights illuminate in red because they are important to the overall vehicle operation.

It is very important to monitor these warning indicators, because they directly relate to charging system performance. On some vehicles as a bonus they provide an ammeter or volt meter gauge in addition to a warning indicator light.

This will allow the driver to monitor the charging system performance more accurately. A positive charge indication on the gauge allows the driver to know that the alternator is doing its job and charging the battery.

Alternator Warning Light

The warning indicator light is the simplest and most common method of monitoring the alternators output. When the alternator warning light is turned on it’s an indication that the charging system is failing to supply sufficient current to the battery.

inside a car battery — Inside a car battery

Also remember when the ignition switch is first turned on this light will also come on because the engine is not running and the alternator is not providing current or voltage. This is known as the bulb check function. The alternator warning lights should go out after the engine is started.

If the light does not go out it could indicate a problem with the alternator itself. Although this would be the most common reason for the light to come on and stay on other problems in the system may cause a false indication of a problem. Depending on the vehicle, a faulty relay or wiring connection can also turn on the alternator warning lights.