Battery Lights On

Why Car Battery Lights On?

Most drivers have experienced battery lights on, and the immediate reaction is that the car battery is dead. In a way, it indicates that the car battery is in poor condition, but it also indicates that your car alternator/voltage regulator might be the culprit of the poor battery condition.

Many drivers underestimated the importance of the car alternator. A car alternator is the major component that supplies power to all car electrical components when the engine is running. It also needs to recharge the car battery at the same time. When the alternator fails, or the alternator belt slips, the car will fail to receive the power it needs. The car will in turn starts to draw power from the car battery instead of charging it. Thus the battery lights on.

Is it safe to drive when car battery lights on?

It very much depends on the state of the car alternator. If the car alternator is just low charging, you should have no problem to drive all the way to your mechanic. To do this, you will need to immediately switch off as many electrical components as possible, such as air conditioner, radio, headlights, etc. Do not switch off your engine until you have reached your mechanic. However if the car alternator is totally failed, you will still have the risk of engine stalling during driving. At that time, a tow truck will be inevitable.


It is always a good idea to periodically check your car alternator condition during your periodical service of your car. It is a simple process by hooking up a voltmeter to check its voltage when engine is running.

However do take note that a wrong alternator checking method will cause you a premature dead battery. Some mechanics tend to just do a simple test by removing the negative cable from the battery when engine is running. If engine continues to run without stalling, then they will declare the alternator is running well. In a way this method can only detect if the alternator is totally failed. If the alternator is just low charging, then this method will be ineffective. For example, when an alternator is low charging below 13V, the engine will continue to run without stalling. However the low alternator voltage is definitely not charging the car battery properly. Thus this method will lead the drivers assuming their alternators are working well, but end up with a dead battery eventually.

If you have trouble finding which battery type suits for your car, do refer here to check up on the car model vs battery type.

If you need guidance on how to DIY for battery replacement, do check out the video here.


Why Car Battery Lights On? Common Causes.

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One thought on “Why Car Battery Lights On? Common Causes.

  1. Great article. Finally an explanation of why my battery has been dying every 2 years: my roundtrip commute is an average of 10 miles per day in city traffic. Then, when I park, I pop open the trunk for a few minutes while I unload items – thereby, runnng the interior lights.

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