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Hyundai Accent 2009 - Battery warning Light

I have a 2009 Accent with 8800 miles on it. The battery warning kept coming on while I was driving, took it to Hyundai dealship and they said the alternator had an issue and they replaced it. The day I brought the car back from the dealership the warning popped up again, took it back to them and they kept my car for a week and finally told me there was an issue with ground.Its been a month and I finally thought it was resolved until 2 days back it popped up again. I don’t know if it makes any sense but the warning showed when I turned on the heater and the rear defroster on. Once the warning light came on, now even if the rear defroster is not on my battery warning light comes on. It doesnt show up every time I start the car but frequently. Sometimes when the warning light is on the rear defroster does not work. What could it be?

I would say it’s time to thoroughly test the battery.
Depending on when your car was built, the battery might already be over 4 years old.
If it is over 4 years old, I recommend replacement.
4-6 years is typical lifespan for car batteries.
No alternator is capable of performing its job correctly if the battery is bad.

Just today I replaced a bad battery on a truck.
Charging voltage with bad battery 13.8v
Charging voltage with new battery 14.4v

Very good info about the problem. From what you stated it sounds to me the shop was on the right track in looking for a bad ground causing this trouble. When added current load is made to run on a bad ground then there is more voltage drop caused across the bad ground connection. This reduces the amount of available power supply voltage from the battery to run the devices in series with the bad ground in the circuit. It is pretty simple to see if that is the problem and a number of tests you could do to prove it is a bad ground. You can even add temporary extra grounding jumpers to see if that clears the problem. If adding the ground jumpers makes a difference I would first clean all the grounds I could find in the engine compartment to see if that fixes things. There could be an issue with a connector causing this trouble also so that may need to be checked. You may want to find a shop that specializes in electrical problems since finding this trouble shouldn’t be much problem for an expert electrical trouble shooter.