How to charge and care for a car battery

A car battery is a bit like the family pet dog. With the right care and attention, it will be faithful and obedient. But drivers who don’t give it a moment’s thought could find it lets them down and goes flat when they need it the most. And unfortunately, that’s most of us: a flat battery is one of the most common causes of car breakdowns for Green Flag members, and the most common in winter.

That goes some way to explaining why this Thursday (18 February) has been named National Battery Day. Knowing how to care for a car battery means knowing how to charge it from time to time. Researching the charging process will throw up all manner of well-meaning amateur and professional advice with conflicting guidance. So this guide is intended to help drivers understand how to better care for their car and charge its battery.

A flat battery is the most common breakdown cause in winter

Green Flag’s technicians know all about the stresses and strains that winter weather can place on a car battery. In December and January, typically around 500,000 drivers are recovered by Green Flag, and the most common cause of their car breaking down is a flat battery.

A car battery loses its ability to hold a charge

Car batteries aren’t designed to last the lifetime of the vehicle. Slowly but surely, a car battery will lose its ability to hold charge. Then at some point, usually between five and eight years old, it won't be able to supply the current required to turn the starter motor that gets the engine going. Car batteries lead a hard life powering on-board systems such as headlights, climate control, windscreen wipers and sound system. On short drives this means that the alternator, which charges the battery from the engine, won't have the capacity to fully recharge the battery. This is a bit like drawing money out of a bank account without ever putting any back in: eventually the bank, or in this case battery, will say 'no more'.

Keep a battery healthy and recharge it fully

To ensure your car’s battery doesn’t let you down the older it gets, it pays to treat it to a full recharge from time to time. The simplest way to do this is to use a trickle charger, which is an affordable and intelligent charging device that actively monitors the health of a car battery and slowly releases a small amount of charge to keep it in tip-top condition.

How to choose a battery trickle charger

Before you buy a trickle charger, read your vehicle’s handbook and check what type of battery it has, and whether or not the car maker recommends against using a trickle charger. If you can use one, you’ll be able to buy online, or from any car care store or – often enough – from the franchised car dealer’s parts department.

Intelligent trickle chargers, also known as smart chargers, are physically small which makes them portable. They plug into a 13 Amp household socket, and normally have a pair of ‘crocodile clips’ that attach to the negative and positive terminals of the car battery.

They often alter the voltage when charging to provide as much current as the battery can safely take. This makes them quick, efficient and best able to restore life into an old or dead battery.

Look for chargers than offer 1 Amp and 2 Amp settings. The former is for small batteries, typically fitted to motorbikes or large lawnmowers. The latter is suited to a car battery. Also, a practical tip is to check that the length of all the charger's cables will work in your home environment and with your car, especially if the battery is on the far side of the car to where the device plugs into the household power socket.

Auto Express motoring magazine tested and rated 12 chargers here.

How to use a battery trickle charger

Read any trickle charger’s instructions before attaching it to a car battery. It’s best to use it when the engine is cold, so if you’ve just been using the car, allow it to cool after switching off. Before plugging the charger into the household power supply, attach the positive (red) and negative (black) clips to the battery terminals. Then switch to the appropriate power setting (2 Amps) and turn on the mains electricity supply.

The unit should switch itself to standby once the battery is charged, but it’s sensible to check it from time to time, if only because the crocodile clips can slip off the battery terminals.

Read more: How to jump start a flat car battery