Car Batteries in Perth Summer Heat: What to Check

This guide is for Perth drivers who want their battery to survive summer and still start the car when the weather cools down. It explains what heat does to a battery, the signs of a battery on its way out, which types suit hot conditions and the checks worth doing before December.

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How hot a Perth summer really gets

Perth summers are long, dry and reliably hot. At the Bureau of Meteorology's Perth Metro station, the average maximum is 31.4°C in January and 31.7°C in February, and even March averages close to 30°C. Those are averages. The same station records about 27 days a year at or above 35°C, and around four days a year at or above 40°C. Its highest reading is 44.5°C, set on 26 February 1997.

You can check the long-term figures yourself in the BOM's climate statistics for Perth Metro. The important point for your car is that the hot season does not end in February. Hot days start appearing in November and can still turn up in March, so a battery in Perth spends close to half the year working in heat.

What heat does inside a battery

A lead-acid battery makes power through a chemical reaction between lead plates and an acid electrolyte. Heat speeds that reaction up. That sounds helpful, and on a hot morning the car may even crank a little faster. But heat also speeds up the slow damage that happens inside every battery: the positive plates corrode, water is lost from the electrolyte, and the battery loses charge faster when the car is parked.

The engine bay adds to the problem. Under the bonnet, the battery sits close to the engine, the radiator and sometimes the exhaust, so it runs well above the air temperature once the car has been driven. Park that car on a sunny driveway or in an open shopping centre car park in the afternoon and the heat soaks in rather than escaping.

Here is the catch that surprises many Perth drivers. Summer does the damage, but the failure often shows up later. A battery weakened by months of heat may still start a warm engine easily, then struggle on the first cold morning in May or June when the engine is harder to turn over and the battery has less to give.

Warning signs to look for

Most batteries give some warning before they fail. Watch for these signs, especially after a run of hot days:

• The engine cranks slowly or sounds laboured, even briefly.
• Interior lights or the dash dim noticeably when you start the car.
• The battery case looks swollen or bulging at the sides.
• A rotten egg smell near the battery, which can mean it is overcharging or overheating.
• White or green powdery build-up on the terminals.
• The stop-start system stops working, or the car shows a battery or charging message.
• The battery is several years old and you don't know its history.

Choosing a battery that copes with heat

When it is time to replace a battery, match it to the car first. Check the size, terminal layout, cold cranking amps and, above all, whether the car has stop-start. Stop-start cars are designed for an enhanced flooded battery (EFB) or an AGM battery, and fitting a basic flooded battery can lead to early failure and warning lights. Some newer cars also need the new battery registered with a scan tool so the charging system knows it has been replaced.

Beyond that, a few things help in a hot climate. Sealed maintenance-free and AGM batteries don't need topping up, which suits drivers who never open the bonnet. AGM batteries tolerate cycling well, but they are not immune to heat and can be damaged by charging voltages that run too high. A battery mounted in the boot or under a seat, as in some European cars, is usually an AGM and should be replaced with the same type. Our guide to car battery types explains the differences in plain terms.

Checks to do before summer

October or November is a good time for a quick battery check, before the hottest weeks arrive. None of these jobs take long.

• Check the battery is held down firmly. A loose battery vibrates and fails sooner.
• Look at the terminals. Clean off any corrosion and make sure the clamps are tight.
• Measure the resting voltage with a multimeter after the car has sat for a few hours. A healthy, charged battery reads around 12.6V.
• Get a load test or conductance test done if the battery is more than a few years old.
• If your battery has removable caps, check the electrolyte level and top up only with distilled water.
• Make sure any heat shield or battery cover that came with the car is still in place.

Don't forget the charging system

A battery can only be as healthy as the system charging it. If the alternator puts out too little, the battery never fully recharges. If it puts out too much, the battery overheats and loses water, which is the last thing it needs in a Perth January. A faulty voltage regulator, a slipping drive belt or a poor earth strap can all cause charging problems.

If your battery warning light comes on, or a new battery goes flat within months, have the charging system tested rather than just swapping batteries. Our guides on testing a car battery and knowing when an alternator needs replacing walk you through the basics.

If the car won't start on a hot day

A car that won't start in a hot car park is more than an inconvenience. Cabins heat up fast, so never leave children or pets in the car while you sort it out, and find shade and water for yourself. If you jump start the car, follow the correct order of connections and keep sparks away from the battery. A battery that is swollen, leaking or very hot to touch should not be jump started. Our guide to jump starting a car safely covers the steps.

Once the car is running, drive straight to somewhere the battery and charging system can be tested. A battery that has failed once in the heat is likely to fail again.

Getting a battery tested around Perth

Many mobile auto electricians will test and replace a battery where the car is parked, whether that is at home or at work. If you are in the northern suburbs, start with our North page, which covers areas such as Joondalup. South of the river, see our South page.

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Questions Perth drivers ask

How long does a car battery last in Perth?

There is no fixed figure, because it depends on the battery type, how the car is used and how well the charging system works. Heat speeds up internal wear, so batteries in hot climates like Perth's often don't last as long as they would somewhere cooler. Have your battery tested each year once it is a few years old, ideally before summer.

Why did my battery fail in winter if heat is the problem?

Heat causes damage that builds up over the summer months, such as plate corrosion and water loss. The battery may still start a warm engine without trouble. When the weather cools, the engine needs more effort to crank and the weakened battery has less capacity to give, so the failure appears in the first cold weeks rather than in January.

Is an AGM battery better for Perth's heat?

An AGM battery is sealed, needs no topping up and handles repeated cycling well, so it suits many cars. It is required in some stop-start and European cars. But AGM batteries still wear faster in heat and can be damaged by high charging voltage. The best choice is the type and size your car's maker specifies.

Should I park in the shade to protect my battery?

Yes, where you can. Shade, a carport or a garage keeps the engine bay cooler after the car is switched off, which reduces the heat the battery soaks up. It won't stop wear altogether, because the battery also heats up while you drive, but it helps, along with keeping terminals clean and the battery firmly clamped.

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