Car Batteries and Western Sydney Heat: Penrith to Parramatta

This guide is for drivers, tradies and fleet operators in Penrith, Blacktown, Liverpool, Campbelltown and the rest of Western Sydney. It explains why summer heat out west is hard on car batteries, how to test yours, how to pick the right replacement and how to park so the battery lasts longer.

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How much hotter Western Sydney gets

If you have driven from the beach to Penrith on a summer afternoon, you have felt the difference. The sea breeze keeps the coast cooler, but it often doesn't push far enough inland to help the west. The Bureau of Meteorology's numbers show how big the gap is.

Penrith Lakes averages a January maximum of 30.8°C, against 26.0°C at Observatory Hill in the city. Penrith Lakes also averages about 22 days a year at 35°C or more, and nearly five days at 40°C or more. Observatory Hill, with a much longer record, averages around three days a year at 35°C or more. On 4 January 2020 Penrith Lakes reached 48.9°C, the highest temperature ever recorded in the Sydney basin. You can check the figures yourself on the BOM Penrith Lakes climate statistics page and the January 2020 Greater Sydney summary.

Why heat shortens battery life

A lead-acid battery stores energy through a chemical reaction. Heat speeds that reaction up, which sounds handy, but it also speeds up the wear. The positive plates corrode faster, and flooded batteries lose water from the electrolyte more quickly. Once that damage is done, it can't be reversed.

Under the bonnet it is much hotter than the air outside. A car that has been sitting in a Blacktown or Prestons car park all afternoon, then crawls home in traffic, can cook the battery for hours. Heat on its own rarely kills a battery on the spot. Instead it slowly cuts the battery's capacity, and the failure often shows up later, on the first cool morning in autumn when the engine needs more cranking power.

That is why many people in Western Sydney get fewer years from a battery than friends who live near the coast. A battery that might last several years in a mild climate can wear out sooner when it spends every summer in high heat.

Signs your battery has taken a beating over summer

Look out for these early warnings. Any one of them is a good reason to test the battery before it leaves you stuck.

• The engine cranks more slowly than usual, especially after the car has sat overnight.
• The stop-start system stops switching the engine off at lights.
• The battery case looks swollen or bulged at the sides.
• White or green crusty build-up around the terminals.
• A rotten-egg smell near the battery, which can mean it is overcharging or overheating. Keep away from the battery if you notice it and get it checked.
• The battery is more than three or four years old and has never been tested.

How to test your battery

A basic check needs only a digital multimeter. Let the car sit for a few hours with everything off, then measure across the terminals. A healthy, fully charged 12V battery usually reads about 12.6V or a little more. Around 12.4V means it is partly charged. Readings near or below 12.2V suggest it is low or getting weak. Then watch the reading while someone starts the engine. If it drops a long way, the battery may not have enough cranking power left. Our guide on how to test a car battery walks through each step.

A voltage reading only tells part of the story. A battery can show good voltage and still fail under load. A proper load test or conductance tester gives a much clearer answer, and most auto electricians can do one quickly. If the terminals are dirty, clean them first, because corrosion can make a good battery look bad. See how to clean corroded battery terminals for a safe method.

Choosing a replacement battery

Start with what the car came with. Match the physical size, terminal layout and hold-down style, then match or beat the cold cranking amps (CCA) and reserve capacity. A battery that is too small for the job will work harder and wear out faster in the heat.

If your car has stop-start, it was built with either an EFB (enhanced flooded battery) or an AGM (absorbent glass mat) battery. Replace it with the same type or the type the manufacturer allows. A standard flooded battery won't cope with the constant restarts and can fail early. An AGM can usually replace an EFB, but an EFB should not replace an AGM. Some newer cars also need the new battery registered to the car's computer with a scan tool so the charging system treats it correctly.

Our guide to car battery types explains the differences, and how to replace a car battery covers the swap itself, including keeping memory settings.

Parking and care tips for hot days

You can't change the weather, but you can cut how much heat the battery soaks up.

• Park in shade, a carport or an undercover car park when you can. On a 40°C day out west it makes a real difference.
• Facing the bonnet away from the afternoon sun helps a little at home or work.
• Make sure the battery hold-down is tight. Loose batteries vibrate, and vibration plus heat wears them out faster.
• Keep the top of the battery clean and dry so it doesn't slowly discharge across the surface.
• If the battery came with a heat shield or insulating sleeve, refit it after any work.
• Test the battery at the end of every summer, not just when it fails.

Getting help in Western Sydney

If you'd rather have someone else test or replace the battery, auto electricians across the west can check the battery and the charging system together. That matters, because an alternator that overcharges will also cook a battery in the heat. Browse our local pages for Penrith, Blacktown and nearby areas to find help close to home or work.

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Questions Sydney drivers ask

Do car batteries really wear out faster in Western Sydney?

Heat speeds up the chemical wear inside a lead-acid battery, and Western Sydney has many more very hot days than the coast. BOM figures show Penrith Lakes averages about 22 days a year at 35°C or more. So a battery in the west is likely to age faster than the same battery kept near the beach, especially if the car is parked in full sun.

Is an AGM battery better in hot weather?

AGM batteries are sealed, so they don't lose water the way flooded batteries can, and they handle deep cycling well. They still age in heat, though, and they cost more. The most important thing is to fit what your car needs. If the car came with an AGM, stay with AGM. If it has a standard battery and no stop-start, a quality flooded battery of the right size is usually fine.

Can I put a normal battery in a stop-start car?

It isn't a good idea. Stop-start cars restart the engine many times on every trip, and they are designed around EFB or AGM batteries that handle that work. A normal flooded battery can wear out quickly and the stop-start system may stop working. Check the owner's manual or the old battery's label and replace it with the same type or one the manufacturer approves.

How often should I test my battery in summer?

A good habit is to test it at the start and end of each summer, and any time the engine cranks slowly. If the battery is more than three years old, test it more often. A quick multimeter check at home is a start, but a load or conductance test gives a more reliable answer about whether the battery will last through the next cold morning.

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