Short Trips, Freeway Traffic and Flat Batteries in Perth

This guide is for Perth commuters and families whose battery seems to struggle even though the car is used every day. It explains how short trips, stop-start freeway traffic and all-day parking at train stations affect your battery and charging system, and what you can do about it.

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A car used every day can still be undercharged

It seems logical that a car driven daily should have a healthy battery. But what matters is how much charge goes back in compared with how much comes out. Starting the engine takes a big gulp of energy, and the alternator needs time at reasonable engine speed to replace it.

Perth's suburbs are spread out, but many daily trips are short: the school run, a drive to the local shops in Cannington or Joondalup, a hop to the station. A five or ten minute trip, especially with headlights, wipers, the fan and the rear demister running, may not put back what the start took. Repeat that day after day and the battery slowly runs down without you noticing.

Freeway peaks are not the long drive they look like

A run down the Kwinana Freeway or Mitchell Freeway in peak hour can take a long time, but much of it is spent crawling or idling. At idle, many alternators produce less current, while the car's demand for power stays the same or rises. Air conditioning or heater fans on high, heated seats, headlights, a phone charger and a dashcam all add to the load.

On a cold, wet evening in queued traffic on the Graham Farmer Freeway or Tonkin Highway, the battery can actually be supplying part of the load rather than charging. That doesn't harm a healthy battery for one trip, but combined with short trips through the week it adds up.

Smart alternators and stop-start engines

Many newer cars have a smart alternator, which varies its output depending on the battery's state of charge and driving conditions. To save fuel, it may charge less when you are cruising and more when you are slowing down. These systems rely on a battery sensor and expect a particular battery type. Our guide explaining what a smart alternator is covers the basics.

Cars with idle stop-start, which switch the engine off at lights and in queues, restart the engine many times on a trip. They use heavier-duty AGM or EFB batteries built for it. When the battery is getting tired, stop-start often stops working first, because the car protects the battery for the next start. If your stop-start has quietly stopped switching the engine off, that can be an early sign the battery needs testing.

Replacing a stop-start or smart alternator battery with the wrong type, or without registering it where the car requires it, can shorten its life and cause charging problems.

Cars parked all day at the station

Plenty of Perth commuters drive to a train station on the Joondalup or Mandurah line, park for the day and then drive a short distance home. That pattern combines the two hardest things for a battery: a short trip and a long rest. While parked, the car's modules, alarm and any accessories keep drawing a small amount of power.

Hardwired dashcams in parking mode, aftermarket trackers and phone chargers left plugged into a live socket can add to that drain. If your car struggles to start after a day at the station car park but is fine at home, a parasitic draw is worth checking.

Longer commutes have their own catches

Living on the fringe and driving 40 minutes into the city doesn't guarantee a healthy battery either. A long commute that is mostly stop-start traffic gives the alternator less chance to recharge than the distance suggests. And on wet winter mornings and evenings you may have headlights, wipers, demister and fan all running for the whole trip, which leaves less of the alternator's output to recharge the battery.

Commuters who park at a station and finish with a three-minute drive home get the worst of both. So do tradies who make many short stops through the day, starting the engine a dozen times between jobs. If that sounds like your week, a battery and charging test every year is cheap insurance. Many batteries give little warning before they fail, and a weak one is far easier to replace in your driveway than in a freeway breakdown lane.

Signs your battery is losing the battle

These signs can also point to the starter motor, poor connections or the alternator. Our guide on whether it's your starter motor or your battery can help narrow it down.

• The engine cranks more slowly than usual, especially on cold mornings.
• Stop-start no longer works or works only occasionally.
• Interior lights dim when you start the car.
• The car's clock, radio presets or window settings reset.
• Warning lights flash briefly or you get odd electrical messages on start-up.
• The battery is more than three or four years old and has never been tested.

Simple ways to keep your battery healthy

• Once a week, take a longer drive at steady speed, ideally 30 minutes or more outside peak hour.
• Turn off the rear demister, heated seats and high fan speeds when you no longer need them.
• Unplug accessories when the car is parked, and check whether your car's power sockets stay live.
• If the car mostly does short trips, use a quality smart charger every few weeks. See how to charge a car battery.
• Keep battery terminals clean and tight.
• Have the battery and charging system tested once a year, and before a long trip.

When to get the charging system checked

If a new battery goes flat within a few weeks, the battery probably isn't the problem. A failing alternator, a slipping belt, a poor earth or a parasitic draw can all flatten even a good battery. If the battery warning light comes on while you drive, read battery warning light on while driving and get it checked soon.

An auto electrician can test the battery under load, check the alternator's output at idle and at higher revs, and measure the draw with the car asleep. Commuters on the northern corridor can start with our Wangara and Balcatta pages, while those heading south can look at Jandakot or the Kwinana and Rockingham area.

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Questions Perth drivers ask

How long do I need to drive to recharge my car battery?

There's no single answer, since it depends on the battery's condition, the alternator and the electrical load. As a rough guide, a short trip of five to ten minutes often doesn't replace what starting used. A regular longer drive at steady speed helps, and a smart charger is the most reliable way to fully recharge a battery that does mostly short trips.

Does sitting in freeway traffic drain my battery?

It can reduce charging. At idle or crawling speed, many alternators produce less current, while lights, fans and accessories keep drawing power. In heavy traffic with lots of electrical load, the battery may supply part of the demand. A healthy system copes, but combined with lots of short trips it can leave the battery undercharged.

Why has my car's stop-start stopped working?

Stop-start usually switches itself off when the car's battery sensor decides the battery's charge or health is too low to guarantee a restart. It can also be disabled by cold, high electrical load or a door or seatbelt sensor. If it has stopped working for weeks, have the battery tested. A stop-start car needs the correct AGM or EFB battery.

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