Flat Car Batteries and Charging: A Quick Guide

When a battery loses enough charge that it can no longer provide the power needed to start your car, that battery is considered flat.

It’s one of the most common reasons why cars don’t start, but a flat battery does not automatically mean you need a replacement. In fact, batteries can often be recharged and still be useful for years, depending on what caused it to go flat and the condition of the battery.

This guide covers everything you need to know about flat batteries. It answers questions about recharging a flat battery, whether driving helps, how long charging takes, why your battery keeps going flat, and how to access mobile battery service across NSW and the ACT.

Can you recharge a flat car battery?

If your battery has some charge left, the car’s alternator (provided it works) will recharge the battery as you drive.

On the other hand, if the battery is flat, a jump start can provide enough power to get the engine going. Once the car is started, a long drive (ideally around 30-45 minutes) should help recharge the battery through the alternator.

Problems may arise with an old or damaged battery, or one with a faulty cell, which may not hold a charge no matter how many jump starts it gets. So, if your car battery keeps going flat after charging, call the NRMA to have your battery checked. If you’re a member, this service is free.

NOTE: Jump starts can seem like a do it yourself thing, but they carry a significant cost risk in newer car models. If you’re not sure about jump-starting your car, it is safer to contact the NRMA and have an expert come to you.

Does driving your car recharge the battery?

Yes. Whenever you drive, your battery gets charged by a device called an alternator. In cases of a flat battery, once you can get the car started, the alternator is able to then generate enough electricity to recharge that battery, while at the same time powering the car.

A quick trip around the corner is usually not enough to generate the required charge. In fact, short drives, stop-start traffic and cold starts drains your battery faster than the alternator replaces the charge, especially with headlights and heating or AC running. Buckle up and hit the road for between 30 and 60 minutes if you can.

How long does it take to recharge a flat car battery?

There’s no fixed number. It depends on how flat the battery is and how you charge it. If you use a mains battery charger, a flat battery can take several hours to reach decent to full charge.

If you recharge using the alternator by driving, the process is slower and may not completely top up a very flat battery, making a mains charger a more reliable option. Your NRMA Patrol will be able to give you some advice when you call them to charge or replace your battery.

I've recharged my car battery but it keeps going flat

There are three reasons why a recharged battery loses power quickly.

• The battery: Older batteries or those with faulty cells struggle to hold a charge.
• The charging system: A worn alternator would not be able to deliver enough charge to the battery, no matter how far you drive.
• A power drain: Batteries drain fast if there’s a faulty component or a disconnected accessory. This happens when the car is off.

You can use your membership to get your battery health checked for free and find out if the fault is with your car’s charging system or with the battery itself.

Why did my car battery go flat, I haven't driven it in several weeks?

Car batteries can lose charge when the car is not being driven. Leaving a car parked for a couple of weeks can be enough to drain the battery.

Here are a few reasons why:

• Modern cars are never fully turned off: Some systems such as the security system, central locking and clock continue to use a small amount of power while the car is parked.
• Mistakes drain the battery: Leaving the headlights or interior lights on, not properly closing a door or the boot, or leaving an electrical accessory plugged in can all use up the battery's charge.

An older or weaker battery holds less charge, so it can go flat faster when sitting, and cold weather can speed this up. If you are going away, an occasional drive can help keep the battery charged.

Does a flat car battery mean I need to replace it?

No, not all the time. A flat battery may still have plenty of life left. It can sometimes be a one-off, caused by a light left on, a long parking spell, or a cold snap. A recharge or jump start will get you going again.

On the other hand, if your battery:

• Goes flat repeatedly
• Struggles to start even after charging, or
• Is more than three years old

It may be time to consider a new battery, as these warning signs can point to a battery that is wearing out. To be certain, a battery test can show the state of the battery and whether it can be saved. If you’re a member, call 1300 726 751 to book a time.

How do I contact a mobile battery service in NSW?

If your battery is flat or worn out completely, our mobile battery service will come to you, 24/7 across NSW and the ACT.

One of our friendly Patrols will come to your home, workplace or roadside location, test the battery, and recharges or replaces it as needed.

You can book a battery replacement online for a time that suits you, or call if you have broken down. Our service runs in metro Sydney, Newcastle, Wollongong, Canberra and much of regional NSW, 24/7, 365 days a year for both members and non-members.

If you break down interstate, you can still contact us and the local motoring club will attend under a reciprocal agreement.

Get your car moving again

A flat battery is fixable, but if it keeps happening it is worth finding out why. A battery test takes the guesswork out of it so you can make necessary repairs to your vehicle or get a new, more reliable battery.

If you’re a member, request a free battery health check and one of our Patrols will come to you. If you are not yet with a member, joining gives you peace of mind that help is never far away when you need it, no matter where you are in Australia.

Book online or call 1300 571 746 to arrange a battery check or replacement for your vehicle.