Battery’s Good, But the Car Won’t Start. Now What?

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Car battery being tested/Image Credit: mikrob111 on Pixabay

When your car won’t start, the first thing to do is check the battery. The vast majority of the time when a vehicle refuses to start up, the cause is a battery with little or no juice. However, sometimes it isn’t that easy. If the battery terminals are clean and properly connected, and a battery tester shows that it’s in good shape, you’ll need to keep troubleshooting to find the problem.

This diagram is a little basic and out of date, but it roughly explains the components of a typical 12-volt charging system:

Automotive starting system/Image Credit: ResearchGate

The battery is a vulnerable component because it can be weakened by age, temperature, and even vibration. But it’s not the only component that needs to be inspected and replaced, and as the years have gone by, it’s become one of the more expensive components in the charging system. There was a time when $75 would buy the best battery on the shelf. These days, you’re looking at $140 to $200.

You don’t want to spend that money unless the battery truly is the problem. We’re not only going to describe how to test these components but the order in which you should be testing, which will uncover typical problem areas and save you from spending more than you have to.

Equipment

You’re going to need a few diagnostic tools, but we’ll keep it to the absolute minimum.

The first thing to consider purchasing is a battery tester with a load tester. This kind of tester not only tests the state of charge at rest but also the health of the battery while it’s subjected to the load of a start cycle.

CEN-TECH 100A 6/12v Battery Load Tester/Image Credit: Harbor Freight

There are fancier electronic testers, but this old-school analog tester has a couple of advantages:

  1. You can usually buy one for less than $40.
  2. It doesn’t require batteries to operate. This thing is going to be hanging in your garage — unused — for years. (Something that requires a fresh set of AAs is going to fail when you need it to work most.)

If you don’t want to invest in a battery tester like this, you can always bring the car — or just the battery — to a good auto parts store. Most have a battery tester that can immediately tell you whether or not your battery is the problem.

The other thing to consider is a decent multimeter. You can spend a ton of money on one with features you’ll never use. Find one in the $29 to $45 range with a large digital readout and you should be fine.

Klein Tools MM400 Digital Multimeter/Image Credit: Klein Tools

This Klein Tools auto-ranging multimeter is about $50 and has all the features you’ll need. It’s available at big box home centers, so you won’t have to find one at a specialty electronics warehouse.

One note: a multimeter can test the voltage of a battery, but it won’t run a one-person start cycle on it the way a battery tester will, so we’d recommend getting both. You can have a second person start the car while you hold a multimeter’s probes against the battery posts, but it’s not as convenient.

The other thing every garage needs is a battery charger. Trickle chargers have gotten smaller, cheaper, and more sophisticated over the years. You can pick up a Black+Decker charger that you simply plug in and not think about for around $30.

Black+Decker Trickle Charger/Image Credit: Black+Decker

Testing in Order

If you want to make this as expensive as possible, just start replacing parts without knowing if they’re the problem.

If you want to get out of this as inexpensively as you can, you need to test a few components to find the root of the problem. We’ve laid these tests out in order of (a) ease, (b) expense, and (c) likelihood of failure.

1. Test the Battery

Even if it’s new, you need to understand what’s going on with the battery. Attach the tester to the battery. If the needle’s not moving at all, then you’ve got a dead battery. What’s more important is its condition under load.

By pressing the “Load Test” button, you’re simulating a start cycle. The battery should be able to hold 8.5 volts for 15 seconds at 0 degrees Fahrenheit. If it doesn’t, then you know the battery is at least part of the problem.

If it does, then you need to start investigating elsewhere.

2. Test the Cables

Battery cables go bad all the time. Not only do the connections get crusted up with corrosion, but that corrosion can creep down inside the cables, rendering them all but useless.

A voltage drop test can tell you if your battery cable is the problem. Using the Voltage setting on the multimeter, first, touch the probes to the battery terminals to determine the voltage of the battery. A fully charged battery should have about 12 volts ready to go.

To perform a voltage drop test of the cables and terminals, touch one probe to the battery post, and then the other to the terminal. It should read at or near zero. If it’s reading any lower (the numbers will be represented as negative decimals: -0.07, for example), then you’re losing voltage in your cables.

Watch this video for a more detailed explanation:

3. Check the Belt

If the battery is discharged and the cable connections are good, you’ll want to fully charge the battery and start looking at the condition of the charging system.

The second cheapest component in the entire charging system next to the cables is the belt, so let’s look at that next. For decades now, cars have used serpentine belts with idler pulleys that maintain tension. If the belt is squeaking or showing signs of slippage, it might not be allowing the alternator to work the way it should. If the belt hasn’t been changed and it looks cracked, it’s time to replace it anyway.

It’s typically a less than $50 replacement, but you also want to replace the idler pulley at the same time. There’s a bearing in it that will go bad at the least convenient moment. At best, this will lead to a dead car. At worst, it could blow your head gasket. This is because this same belt not only spins the alternator, but also the water pump. They’re easy to replace and don’t cost much more than the belt.

4. Test the Alternator

Typically, if your alternator is no good, it’s going to throw a “CHARGE” light on the dash or show you that you’re not running at 14.3 volts. But, you can’t always count on your dashboard to tell you exactly what’s wrong.

Using your trusty multimeter, you can test exactly how much voltage the alternator is putting out. Simply attach the two probes to the positive and negative terminals of the battery, make sure the probe leads are out of the way of any moving parts in the engine bay, and fire the engine up.

The multimeter should show somewhere between 14.2 and 14.7 volts. If it’s showing less, the battery isn’t being charged as well as it should. This will be especially apparent when you’re running accessories like lights, wipers, rear defroster, and the radio. If it shows MORE than 14.7 volts, the alternator is overcharging the battery and will eventually cook the life out of it.

5. Test for Parasitic Drain

It’s hard to place this test using our hierarchy of ease, expense, and the likelihood of a problem. If you’ve left a light on, that should be easy and free to fix. If you’ve got a short in a hidden wire because a mouse chewed through it, that could be difficult and expensive to diagnose and fix.

In general, though, less-than-obvious parasitic drains aren’t as common as some of the other issues on our list. However, if your battery is discharging overnight — which you’re determining because you’ve charged the battery, then tested the voltage the next morning as described in step 1 — then you might actually have some kind of a constant drain happening.

To perform this test, remove the negative battery cable from the battery. With the multimeter set to the highest amp scale (read your multimeter’s instructions), touch one of your multimeter’s probes to the cable terminal, and one to the battery post.

The readout on your multimeter shouldn’t be higher than 50ma (milliamps). If it’s more than 50ma, you’ve got something that’s drawing power from the battery.

To determine what’s causing that draw, you’ll need to follow the instructions in the video below. The process involves removing and replacing every single fuse in the car one by one until that voltage draw goes to fewer than 50ma.

5. Check the Starter

If the cables, belt, battery, and alternator are okay, then (and only then) start looking at the starter. Testing it requires taking it out, meaning that you’re probably going to end up replacing it anyway. So unless you’re pretty ambitious, you’ll probably end up at a mechanic shop. But by this point, you’ll be able to provide your technician with a lot of information about the condition of your charging system. That means you save the mechanic time which he’d otherwise be charging you for. That’s a small win in our book.

We hope this information helps get you back on the road with as much money left in your pocket as possible. And hey, if you decide your current vehicle is more than it’s worth, we know where you can find a new one.

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Craig Fitzgerald

Craig Fitzgerald

Writer, editor, lousy guitar player, dad. Content Marketing and Publication Manager at BestRide.com.