Car Won’t Start – Do I Need a New Battery or is it the Alternator?

Help! My car is having trouble starting! I think it must be the car battery is dying or could be the alternator. At least I think so, but I’m not sure how to check and certainly don’t want to waste my money on replacing parts that have not gone bad yet. Do I need a new battery, or is the alternator bad?

A simple voltage test on the battery will inform you if your battery is bad or if the alternator is bad. Battery voltage should be between 12.6-12.8 volts when the car is off and between 13.5-14.5 volts when the car is on (since the alternator is charging then). There are also a few ways to check without using a multimeter such as the lights test.

Using a multimeter is the simplest and fastest way to check if the alternator or the battery is the problem. I will explain to you how to use a multimeter to check your battery and alternator and determine which has failed. I will also explain how to check them without the use of a multimeter since many people do not own one. (Although a multimeter is an essential tool that you should consider getting!)

And occasionally a car is dead for another reason and if it cannot be started, then the conventional multimeter test on the alternator is not going to work.

And we will go in order of simplest and easiest steps to ensure that we figure this out as easily and as quickly as possible.

Check the Battery – Is it the Reason my Car Won’t Start?

The first thing to check if you think your battery or alternator have gone bad is to take a look at the battery. This is the simplest fix, simplest to check, and less expensive than having an alternator replaced.

Inspect the Battery Terminals

Ensure that the battery terminals are clean, free of corrosion, and tightly secured. A loose connection, or excessive corrosion can cause your car not to start. Next, check the battery for the age of the battery.

A simple wire brush can be used to clean the battery or a battery terminal cleaner like this one on Amazon only costs $4.99.

Tighten the battery terminals securely and a little trick is to twist as you push the battery cables onto the terminals. Since the terminals are tapered, it will tighten nicely as you push down. Then snug it with a wrench of course.

Check the Date of the Battery

Generally a car battery has a round sticker on it with the month and year. (Mo./Yr.)

The next most common way a car battery is marked is with a marker checking a box indicating the month and year numbers on a calendar type sticker.

Battery manufacturers provide the date of manufacture of the car battery just for this situation. They want you do easily be able to know when the battery must be replaced by simply looking at the date on the battery.

How long does a car battery last?

Car batteries generally do not function longer than 8 years. Very rarely do they last that long but I have heard of a car battery working for up to 10 years. If your battery is more than 6 years old, it is most likely the battery that is the problem and should be replaced right away.

Regardless if it will hold a charge again, even if you charge it back up, it is going to fail most likely in the next few months and by replacing the battery now, you are performing preventative maintenance keeping your car healthy and reliable.

Go ahead and skip all the rest of the steps and just go buy a new battery if it is more than 6 years old.

Pro Tip: Costco has great deals on car batteries! They sell high quality car batteries and sell them for 25% less on average than other auto part stores.

If the battery is newer than 6 years old, it is still possible that the battery is bad, so continue on with these tests.

Test the Alternator with a Multimeter

Alternator shown in the engine bay on the left side of the engine to the right of the dipstick

If you do not own a multimeter, buy this Klein Multimeter on Amazon or head to your local hardware store and pick one up for cheap. I personally own this meter made by Klein and it is user friendly, and has lasted me for more than 5 years. If you are considering it, get yourself a multimeter, it will come in handy several more times in the future for sure!

Plug in the leads into the multimeter in the ground and positive ports.

Turn the multimeter dial to the (V) volts option. This will read voltage.

With the car turned off, connect the multimeter leads to the (+) and (-) terminal of the car battery. It is best if you place the red (+) wire on the (+) terminal of the battery and the ground (-) black wire on the (-) terminal of the battery.

If you put the multimeter wires in the reverse position, the multimeter will simply read a negative voltage and it will not hurt the multimeter.

The battery should read between 12.6 – 12.8 volts.

If it is below this range, place the battery on a charger because we still do no know for certain that the battery is the problem. You must recharge the battery to see if it will hold a charge and perform more tests to the battery and the alternator.

Charge up the battery with a trickle charger.

Check the voltage of the battery again after letting the battery sit. If it does not hold a charge at 12.6 volts, or very close to it, then the battery is bad. Or could potentially be low on water in the battery cells! Read my other article about how to know if a battery is low on water and how to add water to the battery.

With the battery charged, connect it to the car, start it up, and check the voltage of the battery with the car running.

The battery should read 13.5-14.5 volts with the car running because that is what the alternator should produce to properly charge the battery.

If the voltage is below this range, your alternator is bad.

If you find that you do not own things like a multimeter, or trickle charger, head over to my resource page where I have compiled a list of the top tools like these that I have tested and highly recommend to help save you time hunting for a good buy. I have already done that and hope to help you out!

Test the Alternator without Multimeter

If you do not have a multimeter, the best way to narrow down if the alternator has a problem is to check the car battery. Don’t skip the battery steps including: clean the battery terminals, recharge the battery, and check the water levels in the battery.

Charge the battery or install a new battery (buy one or borrow one from another car) and if the car runs for a while, then dies again, your alternator is bad since it did not keep the battery charged.

The next best way to test the alternator without a multimeter is to take the alternator in to an auto parts store where they will plug in a tool (ancd check it for free!)

So if you can get your car there then drive it in to check it for free, otherwise, remove the alternator and take it in!

Magnet test

A simple test that can indicate the alternator is bad, although will not guarantee that the alternator is working perfectly, is the magnet test. The magnet in the alternator is frequently what fails and by placing a steel wrench or other ferrous bit of metal on the pulley of the alternator, you can check that the alternator magnet is still in good working condition.

How Long can I Drive with a Bad Alternator?

Perhaps you are out somewhere and need to get home. If the alternator is bad, how far can you drive the car?

Running on a bad alternator, you will only be able to drive between 1-10 miles. You will only make it as far as the battery stays charged. The alternator passes current though the battery charging it as well as provides electricity to the ignition system providing spark for the engine to operate. Once you run out of battery your car will die.

If the alternator is completely failed, you will only make it a couple miles if the battery is fully charged. Will a partially charged battery, you may only make it a mile.

But, you could be lucky and if the alternator is still functioning, but just beginning to fail, it may provide an intermittent charge and you could make it up to 10 miles limping home with the dying alternator.

Test the Alternator without Starting the Car

If your car has other issues, you may be unable to start the car but still want to know if the alternator is bad.

Auto parts stores will plug in a tool for free to the alternator if you bring it in.

Take it in to AutoZone (they for sure do it and certainly other parts stores will check it for free- you will just have to call them up to find out.)

They can simply plug in the alternator to do a test and even narrow down which parts of the alternator have gone bad

Whether it is the brushes, or the diodes, alternators can be repaired in case you do not feel like spending the extra bucks to buy a new one!

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