Winter Cold Starts and Car Batteries in Hobart

This guide is for Hobart drivers who dread the first properly cold morning of the year, whether you park on a frosty street in North Hobart or a driveway in Kingston. It explains why cold weather catches out tired batteries, what to check before winter, and what to do when the car just clicks.

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How cold Hobart mornings really get

Hobart isn't alpine, but its winter mornings are cool enough to find out a weak battery. Bureau of Meteorology long-term figures for Hobart (Ellerslie Road) put the mean minimum at about 4.7 degrees in July, with mean maximums of only about 12 degrees in June and July. You can see the full table on the BOM climate statistics for Hobart.

Those are city averages. Low-lying and open spots get colder. The Hobart Botanical Gardens station on the Queens Domain averages about 3.1 degrees on July mornings, and in July 2024 the Hobart Airport station near Cambridge dropped to minus 1.6 degrees. If you park outside in a valley or on the Eastern Shore flats, expect frost on the windscreen more often than the city figures suggest.

Then there's kunanyi/Mount Wellington. Snow falls on the mountain most winters, and the City of Hobart closes Pinnacle Road when ice and snow make it unsafe. Locals who drive up for a look after a fresh fall are asking a cold engine and battery to work hard at altitude.

Why cold exposes a weak battery

A lead-acid battery makes power through a chemical reaction, and that reaction slows down as the battery gets colder. So on a frosty morning the battery can deliver less current than it could on a mild afternoon.

At the same time the engine is harder to turn. Cold oil is thicker, so the starter motor needs more current to spin the engine fast enough to fire. Diesels have it harder again, because the glow plugs draw heavily before cranking even starts.

Put those together and a battery that coped all summer can suddenly fall short. The battery didn't fail overnight. Winter just removed the margin that was hiding its wear.

Signs your battery won't see out winter

Watch for these before the coldest weeks of June and July:

• The engine turns over slowly on the first start of the day, then starts normally later on.
• The dash lights dim or flicker noticeably while cranking.
• Start-stop has stopped working, or works less often than it used to.
• You hear a single click or rapid clicking instead of cranking.
• The battery is four or more years old and has never been load tested.
• White or green crusty build-up on the terminals, which adds resistance when you need current most.

Get it tested in autumn, not in a car park in July

The best time to find a weak battery is before winter, while a failed start is just an inconvenience. A voltmeter reading only tells you charge level. A proper load or conductance test shows how much cranking ability the battery has left. Our guide on how to test a car battery explains both methods.

Slow cranking isn't always the battery. A worn starter motor or a poor earth strap can look much the same on a cold morning. If a good battery still struggles, get the starting system checked as a whole.

Winter habits that keep a Hobart car starting

A few small changes make a real difference through the cold months:

Accessories that stay on while the car is parked add to the problem. A dash camera in parking mode, a phone charger left plugged in or an aftermarket alarm can draw enough overnight to tip a borderline battery over the edge on a cold morning. If a car keeps going flat, our guide on why a car battery keeps going flat explains how to track down a drain.

• Use a garage or carport if you have one. Even a few degrees warmer helps the battery in the morning.
• Turn off the heater fan, rear demister, lights and seat heaters before you switch off, so the next start doesn't begin with a heavy load.
• On a diesel, wait for the glow plug light to go out before cranking.
• Crank in short bursts of no more than about 10 seconds, with a pause between tries.
• Mix in a longer drive each week. Short winter trips with the heater and demisters running can leave the battery short of charge.
• If the car sits for weeks, use a smart battery maintainer.

Choosing a replacement for cold starts

Cold cranking amps (CCA) is the rating that matters most here. It describes how much current the battery can deliver in cold conditions. Match or exceed the CCA your vehicle maker specifies, and match the physical size, terminal layout and hold-down too.

Battery type matters as much as CCA. Many cars with start-stop need an EFB or AGM battery, and a basic flooded battery in their place can fail early. Our car battery types explained guide sets out the differences. Some newer cars also need the new battery registered with a scan tool so the charging system treats it correctly. In a hybrid or EV, only work on the small 12V battery and leave the high-voltage system to licensed professionals.

When it won't start on a frosty morning

If the car won't crank, a jump start or portable jump pack will usually get you going. Follow the safe connection order in our jump starting guide and don't try to jump a battery that is cracked, swollen or leaking. Once it starts, have the battery and alternator tested rather than hoping it was a one-off.

If you're stuck at home before work in Glenorchy or the Eastern Shore, a mobile auto electrician can test the battery, starter and charging system in your driveway and fit a replacement if needed. During winter storms, follow SES Tasmania advice on preparing for storms and avoid driving when roads are flooded or blocked.

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Questions Hobart drivers ask

Why does my car start fine in summer but struggle in Hobart's winter?

Cold slows the chemical reaction inside a lead-acid battery, so it delivers less current, while cold oil makes the engine harder to turn. A battery that has lost some capacity can cope in mild weather but run out of margin on a frosty Hobart morning. A load test before winter will usually show the weakness early.

What CCA rating do I need for a car in Hobart?

Start with the cold cranking amps your vehicle maker specifies, which you'll find in the owner's manual or on the original battery. Hobart winters are cool rather than extreme, so meeting or slightly exceeding that figure is normally enough. Make sure the battery type, size and terminal layout also match, especially on start-stop vehicles.

Is it bad to run the heater and demisters on short winter trips?

It's not bad, and clear windows matter for safety. But heater fans, rear demisters and heated seats all draw power, and a short trip may not give the alternator enough time to replace what the start used. If most of your driving is short, add a longer run each week or use a smart charger now and then.

Should I test my battery before driving up kunanyi/Mount Wellington in winter?

It's a good idea if the battery is a few years old. It is colder at the top, and you don't want a slow start in a car park on the mountain. Check the Pinnacle Road status before you go, because the road is closed when ice and snow make it unsafe.

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