The alternator in your car is an integral part of your vehicle's electrical system. If you have a new alternator and the battery is still not charging, then you definitely have some kind of a problem with your battery that you'll need to address immediately. That's because the alternator works in conjunction with your battery to ensure that all your electrical systems have the power they need to function. While you might initially think that any problems with electrical things like lights or radio not working are directly related to the battery, the alternator is actually where most of the power in your vehicle comes from.
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Consider that if you were to leave the lights of your car on overnight by the next day your battery might be drained completely. And yet when you drive routinely with the light on the battery can last for years before needing to be replaced. That's because, when the vehicle is in motion and the engine is running, it's the alternator that's handling the job of running the electrical systems and not the battery.
What is the Alternator in Your Car?
The alternator is essentially a generator and it keeps your battery charged while supplying additional electrical power for the other systems in the vehicle. If you have a new alternator and your battery keeps dying on you, then there's definitely a problem that you're going to need to look into.
The alternator is bolted onto your engine and is driven by a serpentine drive belt. Unlike components such as your oil filter or your water pump, the alternator should last if not the life of your vehicle then definitely a significant amount of time. A good alternator and can last well over a decade, sometimes as long as 15 to 20 years. However, if an alternator does fail on you then you'll know it fairly quickly as your electrical systems will fail soon afterwards. The charge in your battery does not last long without the alternator there to keep it running properly.
Oftentimes when there is an electrical problem you might assume that it's an issue with the alternator but if we've established that the alternator is brand new and functioning properly, then there must be another problem going on. Let's take a look and see what can cause your battery not to charge even when your alternator is working properly.
Bad Battery
The most obvious reason why your battery won't charge when your alternator is brand-new is that the problem is with the battery itself. If your battery has died you can give it a jump start again and let it stay connected to the car that's jumping it for a couple of minutes to make sure the battery is able to develop a good charge. If your car stops almost immediately after the jumper cables have been removed, then your battery is likely incapable of being charged at this point and that's definitely a problem.
If you're not 100% sure, you can use a multimeter, or a voltmeter, to check the current coming from your battery. Attach the positive lead to the positive battery terminal, that's the red one, and then the negative leave it to the black terminal. With the engine off you should be getting a reading of 12.5 volts on your multimeter. They can be slightly off of this but no more than about 0.1 or 0.2 volts. If you're getting less voltage than that, then your battery is not able to hold a proper charge.
Bad Battery Connection
It's possible that if your battery isn't charging and your alternator is working fine that you have an issue with the terminals, or the wiring connected to your battery. In older cars the terminals on your battery may be suffering from corrosion which you can discover with a quick visual inspection. It's also possible that they're even coming loose. Generally, this can be cleaned up with a wire brush and some sandpaper to get rid of the crusty corrosion and get back down to the clean metal again.
It’s less likely that you'll have a problem with the wiring itself but not impossible. Again, a quick visual inspection should let you know if things are okay and if you can see something wrong then you'll know you might need to replace the wiring. Usually wiring that connects to your battery is pretty solid and reliable but depending on the age of a car it's something that you may want to look at. Just remember that in some vehicles it can be hard to see this because of how securely batteries are affixed in the car and you may need to remove a plastic cover to get a good look at it.
Blown Fuses
Fuses in your car only last for so long, and the older they are the more likely they are to just wear out and get brittle with age. When a fuse gets old enough even the stress of starting your car can blow one out sometimes. When the problem is your battery, you can check the fuse for your starter motor and for the alternator to see how they're looking. You'll probably need to refer to your owner's manual or at least Google your make, model, and year of car to find out where to look for these particular fuses since most of us wouldn't know which is which off the top of her head.
If you see either one of these fuses has blown, or even if they're looking a little worse for the wear, then you can pick up new fuses for just a few dollars at any store that sells auto supplies or even your local Walmart.
Aftermarket Accessories
Your car is designed to handle the power requirements of all the accessories that normally come with it and a little bit of extra, but not a lot. You can run the radio, you can keep your headlights on, you can have the air conditioner going and in a pinch you can plug in a little vacuum or maybe charge your cell phone. At some point however you can start including far too many accessories for your battery to be able to handle. There was once a time when some cars came with accessories like an electric shaver installed in the dashboard. All the stress of these random electrical components can be too much for a battery to handle.
While you may not have an electric razor attached to your vehicle right now a lot of drivers have things like aftermarket security systems, Bluetooth, speakers and aftermarket radios, dashcams and other accessories that overtime can cause too much drain on the battery. All of your accessories should shut down when you shut your car down normally, but depending on how they were made some of these may still keep a live connection to your battery 24/7 no matter what your car is doing.
Bad Voltage Regulator
If you are sure that your alternator is working properly and yet your battery is still not charging, then it's possible that you have a bad voltage regulator in your vehicle. The voltage regulator keeps the right amount of electrical power flowing through the various electrical systems in your vehicle. If it breaks and the components in your car's electrical system are going to have a spotty ability to continue working if they work at all.
If the voltage regulator in your car completely fails, then the battery can no longer be charged by the alternator and it will soon lose its charge and die. You could get a jump and get your battery recharged but the same thing is going to happen again fairly quickly as the charge dissipates and once again dies because your car is not able to maintain the battery thanks to the voltage regulator failing. You can get a voltage regulator repaired at a mechanic for probably between $180 and $400 depending on the make, model, and year of your vehicle.
Bad Serpentine Belt
As we said, the serpentine belt is what connects to the alternator. This belt drives the alternator and occasionally the serpentine belt can get worn out or damaged from just general wear and tear or an overheating engine or various problems like that. If your belt has gotten too stretched out or it is getting frayed and is starting to lose its grip, then it will start slipping from the alternator pulley. That means your alternator is not going to be getting power fast enough to keep up with the demands of your vehicle's electrical system.
Oftentimes you'll notice a squealing kind of sound to alert you to a problem with your serpentine belt failing, and also you should be able to see it slipping away if you give me a quick visual inspection. Also, if there is significant wear and tear that's another thing, you'll be able to notice by taking a look at it. When you need a new serpentine belt you're looking at a replacement cost of typically between $25 and $75.
Bad ECU
The engine control unit, sometimes called the engine control module, is sort of like a brain in your car. It's possible your car has several of these managing different functions but essentially all you need to know is that the ECU is a computer that will control most if not all of the electrical systems that are required to run your car. If an ECU fails, and the electrical components attached to it are also going to fail.
Typically, the only way to diagnose a problem with a bad ECU is to use an OBD2 scanner, or an onboard diagnostic tool. Those are usually those yellow boxes that you'll see mechanics using with wires attached to a vehicle to determine why a particular light came on your dashboard. You can buy one yourself from a site like Amazon at a pretty reasonable price if you're interested in doing any kind of diagnostic work on your vehicle. You can get cheap ones for as little as $30 or so, and they range in price up to several hundred from there depending on how elaborate you want the scanner to be.
If you have a problem with the ECU in your vehicle the repair bill could potentially be quite steep. A faulty ECU might end up costing you anywhere between $1,000 and $3,000 to get repaired. Well that seems extremely steep and something you want to avoid, it's also worth remembering that you don't necessarily have to replace an ECU if it goes bad because in many instances these can actually just be reprogrammed so that they function properly again. Getting your ECU reprogrammed is much more cost-effective than might only be between $300 and $700. That's still not chump change, but it's definitely a lot better than $3,000 to swap the unit with a brand new one.
The Bottom Line
The alternator is one of the first places you want to look if it happens that your battery is no longer charging and your vehicle. However, if your alternator is brand new and you know it's working the way it's supposed to then there are clearly a handful of things that you need to look at to figure out what the problem is to get the electrical systems in your vehicle working properly again.
Even if your alternator is brand new, it never hurts to double-check and give it a test to ensure that it actually is working properly. Sometimes even new parts can fail fairly quickly. Scan with your multimeter on to let you know if your alternator is doing what it's supposed to do. As we said, your battery should be reading at about 12.5 to 12.8 volts when your vehicle is off. When you turn it on, the voltage should go up at that point. As long as it does, then it's likely that your alternator is fine, and the problem may be one of the other issues that we have listed here for you to check into.