What should I do if I get a flat battery?

Replacing a lead-acid battery is one of the ‘joys’ of car ownership.

The typical internal combustion engine needs fuel, oxygen and spark to run. And it’s the battery that supplies the spark, as well as the electrical power to crank the engine and power all those comfort, convenience and safety features.

Unlike Russian novels, batteries don’t endure forever. Modern sealed batteries will provide reliable cranking power for quite a while, and it’s not unknown for the battery to remain in service up to six years or longer.

Equally, however, pessimists will tell you that it’s not without precedent for a battery to fail within three years.

Important point here: to avoid being stranded by a flat battery, pay it the attention it deserves. If the person servicing your car tells you that the battery is in danger of failing, get it replaced.

If there’s evidence you can witness for yourself that the battery’s best days are now behind it, have it checked and replaced if necessary.

It’s not common for a battery to fail completely while the car is in operation, but it can happen in extremely tough environments, for instance.

Famed racing driver Sir Stirling Moss nearly died of thirst when the plates in the battery of his Mercedes-Benz 280E shook loose during the North African leg of the 1974 London to Munich World Cup Safari. Moss and his crew were lost and stranded in the heat of the Sahara with a car that would not restart.

In our everyday environment, a catastrophic battery failure usually means little more than running late for work and holding up a lot of your fellow commuters behind you.

First things first, move your car out of the traffic if that’s at all possible. If you can push the car yourself, do so, but never do anything that could compromise your safety or wellbeing, or that of others.

You may be able to enlist the aid of a good Samaritan on foot or a driver in one of the other cars behind you. More information is available here.

If your battery has died and the car has no power whatsoever, you won’t be able to operate the hazard flashers, and nor will you be able to crank the car forward on the starter motor.

Contact your state motoring association or the company that provides you roadside assistance. When they attend, they will sort out the electrical problem – it may be as simple as a lead slipping off one of the battery terminals, rather than the battery expiring.

Alternatively, they will replace the battery at cost to you, if the battery is the root cause of the problem.

Should the electrical problem be something more serious, or your car has a battery of a particular kind that’s not easy to replace on the road, the roadside assistance folk will call for a tilt tray or tow truck to transport your car to your home or a nearby workshop.

If you don’t have roadside assistance, a state motoring association will sign you up on the spot and send out a service person to help you, but it will cost you that year’s subscription.

By the way, that annual subscription is probably the best value insurance money can buy. If you’re not covered for roadside assistance, the question you need to ask yourself is: ‘Why not?’

A battery can steadily lose the capacity to retain charge. There may be no signs, if the alternator is working correctly to recharge the battery while the vehicle is on the move. But this gradual degradation will become apparent if you leave the car parked in the garage for three days and then find there’s not enough kick in the battery for the starter motor to crank the engine for even one revolution.

A healthy battery should be able to retain sufficient charge to start the car after a couple of weeks parked. Anything less is a sign that the battery is getting a bit old.

Leaving a car standing for extended periods can be harmful to the battery, so it’s a good idea to have a ‘trickle charger’ connected to the car’s battery, drawing power from the AC mains power outlet in the garage to keep the car battery fully charged.

When you’ve left a car standing for a while, and find that it won’t start when you need the car to be somewhere, the first impulse for most people is to call on the assistance of a friend or neighbour to help jump-start the car.

Provided you know what you’re doing, you’ve done this before, and you’re prepared to read the owner’s manual to find out the procedure, you should be fine. If you are in doubt for any reason, don’t try it. There’s so much that could go wrong.

If you get confused and connect the positive terminal from one battery to the negative terminal of the other, and vice versa, you’ll soon know about it.

And if it should damage one or more of your car’s on-board computers, you’ll be out of pocket for potentially thousands of dollars.

If you have an older car with a manual transmission, pushing it to start is an option. Not a good option, though.

The trick here is to make sure you have plenty of room in a location where there’s little traffic. If you can start the car rolling on a downhill section of road, that takes much of the back-breaking effort out of the process.

You may opt to push-start the car if you don’t have jumper leads with you at the time, and the car’s alternator light is still shining, so you know there’s some charge remaining in the battery. Perhaps the battery is fine, but the starter motor doesn’t work.

Sit behind the wheel, with the ignition switched to ‘On’. Ask a friend or family member to push the car from behind – making sure you release the parking brake first.

At the point the car has reached a speed above 5km/h, press the clutch pedal to the floor, select second gear and dump the clutch. This should provide enough energy to spin the crankshaft fast enough for the engine to fire and keep running without need of the starter motor.

Note that it’s definitely easier in older cars, with lower-compression engines and lower-ratio final drives... if you want to get technical about it.

Smaller cars are easier to push, of course, since they usually weigh less than 1.5 tonnes. A reasonably fit person can push a car weighing that little at a speed sufficient to turn the engine over.

A word of warning. If you are rolling a car downhill to ‘bump-start’ the engine, be aware that until the engine actually fires and runs continuously, you will not have power assistance for the brakes or the steering.

Why is this method also known as ‘bump-starting’? When the driver pops the clutch, the torque fed back from the drive wheels through the transmission to the engine overcomes the compression bump in one or more cylinders for fuel and air to combust and start the engine.

This is work normally done by the starter motor – start the engine revving fast enough for combustion to maintain an idle speed at least.

It is theoretically possible to push-start a car with an automatic transmission, but only by using another car to push your car up to speed. You may incur damage to the drivetrain and the body panels.

We don’t recommend it – and why go to that sort of trouble when you’ll start the car easier with jumper leads anyway?

More often than not, the battery will provide some warning that it’s on the way out. It could start with slower starter motor cranking on cold mornings, or dimmed headlights at night, or wipers that just crawl across the windscreen.

The battery may not retain charge for more than a day or two of the car left standing.

Reduced charge in the battery is not necessarily a sign that the battery itself is past it. The problem may rest with the alternator – the ‘dynamo’ driven by the engine to generate electrical charge replacing that energy the battery expends to power all the car’s gadgets.

Often low charge shows up when the alternator warning light illuminates in the dash while the engine is running. Sometimes it may glow dimly at idle, or it may burn bright. Whatever the case, there’s a problem that needs your immediate attention.

Even reduced charging – due to a slipping alternator drive belt, for example – will be enough to flatten the battery after a trip to the shops and back at night.

The good news there is that tightening the belt or replacing it is a lot cheaper than a new battery – and the existing battery will usually recover from being undercharged.

If you ignore the signs, the battery will eventually run out of charge, and in serious cases there won’t even be enough charge remaining to supply the spark for the fuel/air charge to combust. In this circumstance, the engine will just stop running – and the starter motor won’t crank at all. You’ll have no lights either – not even hazard flashers.

So the important point there is this: Don’t let the battery get to that point. At the earliest hint of diminished charge, head for home, or the nearest workshop if you’re some distance from home.

Are you a member of a state motoring association? Are you covered for roadside assistance? The motoring association or company covering you for roadside assistance can often replace the car’s battery on the spot.

It will cost you though, and it’s often cheaper to buy a battery from an aftermarket parts retailer – an Autobarn, Repco or Burson Auto Parts store – and fit the battery yourself.

Replacing the battery isn’t hard if you know what you’re doing, but you’ll need some tools.

What to do when you’re stranded with a dud battery

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