It’s probable that the majority of car electrical system faults that trigger the red warning light can be traced to an alternator or battery issue and replacing either or even both (depending on the fault) usually fixes the underlying fault and clears the red warning light.
But what if, the light stays on even after replacing the battery and alternator? What do you do then?
This post explains why this can happen and suggests tips that can you resolve this.
4 Likely Reasons the Car Battery Light Stays On with new Battery and Alternator (+ What to Check)
If the car battery light stays on even with a new battery and alternator fitted, it may be because:
#1. The alternator may not be connected properly or may be defective
Confirm the alternator output voltage is within the expected range. With the car engine running, use a digital voltmeter to measure the alternator output voltage.
For a well-functioning alternator with firm, clean wire connections, the voltage across the battery posts when the car engine is running should be in the 13.5 – 14.5 V range.
If out of range, confirm that the alternator is properly fitted, wired correctly, and that the wire connections are firm and make solid clean contact.
Particularly, inspect the alternator’s positive and ground connections making sure that the alternator is properly grounded and the positive wire connections are solid and firmly connected.
#2. Car battery connections may be loose, damaged, and corroded. Inspect the car battery’s positive, negative, and ground terminal connections for corrosion, and make sure they are not loose.
Either of these issues affects car battery charging which then triggers the battery light. Confirm that the engine ground connection is intact and that there are no voltage drops.
Once you confirm that the battery terminals are clean, and the grounds are intact, firmly connected, check if this clears the battery light.
#3. Inspect the serpentine belt to check that it is in good condition and properly fitted. A loosely fitted or damaged serpentine belt affects the car battery’s ability to charge well and triggers the battery light too.
If the belt is damaged, replace it with another recommended by the manufacturer. Follow the installation guidelines to ensure that its tension is set appropriately.
#4. The replacement car battery or alternator could still be faulty.
If after confirming that the alternator, battery, and belt tests are in good condition yet the battery warning light still persists then the car battery and or alternator may be faulty out of the box.
Take the car alternator and battery for testing at a reputable auto parts store to confirm that they are still in good condition.
Should you Ignore the Battery Light?
No, do not ignore the battery light. It shows that there is still a problem with the car’s electrical system. In ignoring it, you risk getting stuck when the car battery is drained flat or the car battery fails prematurely.
If the battery warning light stays on even with a new battery or alternator fitted, confirm that the battery and alternator wire connections (including the ground) are clean, intact, and firmly connected.
If the problem still persists, test the alternator and car battery at a reputable auto parts store. Do not hesitate to contact a qualified car mechanic.