Won't Start? How to Tell If It's the Battery, Alternator or Starter Motor

The short version

If your car will not start, the cause is almost always one of three things. A flat battery, a failing alternator, or a worn starter motor. Each one fails in a slightly different way, and you can usually tell which one in under a minute by listening and looking at the dashboard.

A 60-second triage:

1. Turn the key (or press the start button) and watch the dashboard. If the dashboard lights are dim or off completely, the battery is flat. If they are bright and steady, the battery is fine and you have a starter motor or alternator issue.
2. Listen for what happens when you try to crank. A single loud click and nothing else points at the starter motor. Rapid clicking points at a flat battery. Slow, laboured cranking that does not catch points at either a weak battery or a worn starter.
3. If the car starts but the battery keeps going flat the next day, the alternator is the suspect, not the battery.

The rest of this article explains each scenario in detail, what causes each fault, what it costs to fix, and what you can safely check yourself before calling us.

The three culprits, explained

The battery

The battery is the rechargeable storage unit under the bonnet (sometimes under the boot floor on European cars and some Holdens). Its job is twofold. It supplies the big burst of current needed to crank the engine over, and it powers all the electrical accessories when the engine is off.

A battery typically lasts three to five years in Brisbane's climate. Heat shortens the life. Short trips shorten it more, because the alternator never has enough running time to fully recharge it.

When a battery is flat or failing, you get:

• Dim or non-existent dashboard lights when you turn the key
• A clicking sound (often rapid) when you try to crank, but no actual cranking
• No reaction at all if the battery is completely dead
• A car that started fine yesterday and is dead this morning, even though you did not leave any lights on

The alternator

The alternator is the device on the front of the engine, driven by the auxiliary belt. Its job is to charge the battery and power the car's electrics while the engine is running. A healthy alternator outputs around 13.5 to 14.5 volts at idle.

When an alternator fails, the symptoms come on slowly over days or weeks. The battery is no longer being recharged on each drive, so it gradually depletes. You typically see:

• A battery warning light (the picture of a battery on the dashboard) that flickers on, especially under load (lights on, indicators going, AC running)
• The car starts fine, but won't start again the next morning
• A jump-start gets the car going, but it dies again within a day
• Headlights that brighten and dim with engine revs (a subtle sign)
• Eventually: the car cuts out while driving, because the battery has emptied and the alternator cannot keep up

The starter motor

The starter motor is the heavy electric motor bolted to the side of the engine that physically spins the engine over when you turn the key or press the button. It draws huge current (typically 150 to 300 amps for a couple of seconds) and lives a hard life.

When a starter motor fails, the dashboard lights stay bright (because the battery is fine), but the engine will not crank. Typical symptoms:

• A single loud "clunk" or "thunk" when you turn the key, then nothing
• A slow, laboured cranking that does not catch
• A grinding noise from the starter (the starter gear not engaging the flywheel properly)
• Intermittent failures: it starts fine three times, then refuses on the fourth, then works again

A failing starter often gets worse in heat (the metal expands and binds), which makes summer in a hot Brisbane car park a classic time for it to give up.

A simple decision tree

Stand at the driver's seat and do this in order:

Step 1: Turn the key to "on" (or press start once without your foot on the brake). Look at the dashboard.

• All dashboard lights bright and normal → go to Step 2.
• Dim, flickering, or missing dashboard lights → battery is flat. The next step is a jump-start or a replacement.

Step 2: Try to start the car.

• Engine cranks (turns over) but does not catch → the starting system is fine, the fault is elsewhere (fuel, ignition, immobiliser). Skip to "If it cranks but does not catch" below.
• Engine cranks slow and laboured → either a weak battery or a tired starter. Needs testing to confirm which. The next step is a charging-system diagnostic.
• A single loud click, no crank → starter motor is the most likely cause. Occasionally a very flat battery. Needs testing.
• Rapid clicking, no crank → flat battery, almost certainly. The starter is trying to engage but the battery cannot deliver enough current.
• Absolutely nothing, dashboard goes dim when you try → very flat or dead battery.

Step 3: If the battery is the suspect, is it dead-dead or just flat?

A "flat" battery (left lights on, parasitic drain, short trips) can be jump-started and will run fine afterwards, though the battery should be tested to confirm it is still healthy. A "dead-dead" battery (over five years old, internally damaged, has been deeply discharged repeatedly) will not hold a charge even after a jump-start. The next drive ends with another flat battery.

What you can safely check yourself

Two things that genuinely help and are safe to do:

1. Check the battery terminals. Pop the bonnet. Look at the two terminals on top of the battery. If you see a powdery green, white or blue crust around either terminal, that is corrosion and it is electrically resistant. Sometimes the engine will not crank purely because of bad terminal contact. The fix: disconnect the battery (negative first), clean the terminals with a wire brush or hot water and bicarb soda, reconnect (positive first).

Note: if you are not confident with the basic tools, skip this. A dropped spanner across battery terminals causes spectacular sparks. Call us instead.

2. Try a jump-start. If you have jumper cables and another car, jump-start it. If the car starts immediately and runs fine, the battery is the culprit. Drive for at least 30 minutes to give the alternator time to recharge it. If the next morning it is dead again, you have either a deep-discharge-damaged battery or an alternator that is not charging.

What not to do:

• Do not try to bump-start (push-start) an automatic car. Automatics will not start this way and you can damage the transmission.
• Do not connect jumper cables in the wrong order. The correct sequence is:
  1. Red clamp to the dead battery's positive terminal.
  2. Other end of the red clamp to the good battery's positive terminal.
  3. Black clamp to the good battery's negative terminal.
  4. Other end of the black clamp to a bare metal point on the dead car's engine (not the dead battery's negative terminal — this avoids igniting any hydrogen gas around the battery). Reverse this sequence to disconnect. If in any doubt, RACQ's roadside guide walks through it with photos.
• Do not crank for more than 10 seconds at a time. The starter motor cannot dissipate heat fast enough, and you can burn it out trying to start a car that has another fault.

What it costs to fix

Typical 2026 prices in Brisbane, for the most common Australian sedans and SUVs:

Job	Starting price
Charging-system diagnostic (battery + alternator + starter test)	$129 (credited against any repair)
Battery replacement, standard sedan or small SUV	$179
Battery replacement, AGM (start-stop car)	$329
Alternator replacement, sedan or small SUV	$450
Alternator replacement, mid-size SUV or ute (Hilux, Ranger)	$650
Starter motor replacement, sedan	$390
Starter motor replacement, mid-size SUV or ute	$550

The diagnostic step is genuinely worth paying for, because the alternative is replacing the wrong part. A workshop that diagnoses-by-replacement will sometimes fit a $450 alternator when the actual fault was a $179 battery, or vice versa. We test on-site with a proper carbon-pile load tester before we recommend anything.

Full pricing detail is on our pricing page.

If it cranks but does not catch

A car that cranks normally (the engine spins over at normal speed when you turn the key) but does not fire up is a different problem. The starting system is fine. The fault is in fuel, ignition or immobiliser.

The common causes in order of likelihood:

• Empty fuel tank. Sounds silly. It happens more than you think, especially on cars where the fuel gauge has been wrong for ages.
• Immobiliser issue. The car does not recognise the key (look for a flashing security light on the dashboard). Try the spare key. If the spare works, the original key fob's battery is dead or the chip in it has failed.
• Faulty crankshaft position sensor. Common on older Mazdas and some Fords. Often comes on suddenly after a hot day.
• Failed fuel pump. Listen for a quiet two-second buzz from the back of the car when you turn the key to "on". No buzz means no fuel pump priming.
• Spark plug failure or coil pack failure on a misfire, severe enough that no cylinder fires.

This is a diagnostic job, not a guess-and-replace job. The codes the engine has logged will usually point straight at the cause.

What to do right now if you are stranded

If you are stuck with a non-starting car right now, three things:

1. Get the car somewhere safe. Out of traffic, off the road, in a flat area. If you are in a hazardous spot (motorway shoulder, blind corner), call roadside assistance first for safety, then us for the repair.
2. Try the basic checks above. Dashboard lights, jump-start if possible, fuel gauge, spare key.
3. Call us on 0451 159 954. We can usually be on-site within a couple of hours across Brisbane, Logan, Ipswich and the Gold Coast. Tell us what you tried and what the symptoms were, that gives us a head start on what to bring.

We carry common batteries on the van, plus a full diagnostic kit. Most won't-start callouts are sorted in the same visit.

The bottom line

A car that will not start is one of the most stressful things your car can do, and one of the most diagnosable. The pattern of how it fails tells you most of what you need to know. Dim dashboard means battery. Single click with bright dashboard means starter. Battery flat again the next day means alternator.

A proper diagnostic costs $129, tests all three components definitively, and is credited against the repair if you proceed. That is meaningfully cheaper than guess-and-replace.

For more on charging system work specifically, see the alternator and starter motor service page. For battery work, the battery replacement page has full pricing and what is included.