Car battery: signs it's dying and what to do in winter

Signs the battery is near its end#

• Slow starting: the starter turns more slowly than usual, especially in the morning.
• Flickering at start-up: the dashboard lights or the screen dim or blink as you start the engine.
• Start-stop stops working: the car no longer switches the engine off at the lights. Many systems switch themselves off when the battery is short of charge.
• Warning messages on the dashboard about the battery or the electrical system.
• Age: the manufacturing date is on the battery's label. An old battery can work fine in summer and give up at the first hard frost.
• Appearance: a swollen, cracked or leaking case, or terminals covered in white-green deposits.

Why batteries fail in winter and how to help yours#

In the cold, the chemical reaction inside the battery slows down, so it delivers less current. At the same time the engine oil is thicker, and the starter needs more power to turn the engine over. On top of that, in winter you use more power: heating, lights, the rear-window demister, heated seats.

• Short trips don't recharge the battery. If you only drive a few kilometres around town, the alternator doesn't have time to replace what starting used. A longer drive now and then helps.
• Switch things off before starting: heating on full, lights, demisters.
• Clean, tight terminals: deposits and a loose terminal look just like a weak battery.
• A car left standing slowly drains its battery on its own. If you don't use it for weeks at a time, a maintenance charger suited to the battery type keeps it topped up.
• A test before winter at a garage or battery shop tells you how the battery is doing before it leaves you stranded in a car park.

Battery, alternator or starter motor?#

The battery starts the engine, the alternator recharges it while you drive, and the starter motor turns the engine over. The symptoms can overlap, so the table below is only a guide:

A garage or an auto electrician tests the battery and the charging system with proper equipment and tells you which part is at fault. Don't replace the battery on a hunch: if the alternator isn't charging, a new battery will go flat too.

Start-stop batteries: AGM and EFB#

Cars with start-stop restart the engine many times on a single trip, so they use batteries built for it: AGM or EFB. The car's manufacturer says which type it needs.

• Fit the type the manufacturer specifies. A conventional battery in place of an AGM or EFB one wears out quickly, and start-stop may stop working properly.
• Check the other figures too: capacity, cold cranking current, size and terminal layout, according to the car's specifications.
• On some cars the new battery has to be registered with the car's computer, so the charging system knows it's new. Ask the garage whether your model needs it.

How to jump-start a car safely#

Read the car's handbook first: some models have dedicated jump-start points, others rule out certain methods. Don't try a jump start if the battery is swollen, cracked, leaking or looks frozen. The basic steps:

1. 1

   Prepare both cars

   Both engines off, ignition off, everything switched off. The cars must not touch.

2. 2

   Red lead

   Clip one end to the positive (+) terminal of the flat battery, then the other end to the positive terminal of the good battery.

3. 3

   Black lead

   Clip one end to the negative (−) terminal of the good battery, then the other end to a bare, unpainted metal part of the engine in the car that won't start, away from the battery.

4. 4

   Start up

   Start the good car, leave it running for a few minutes, then try your car. If a few short attempts don't work, stop and call for help.

5. 5

   Remove the leads in reverse

   First the black lead from your car, then from the good car, then the red one. Keep the engine running and take a drive so the battery recharges.

If the car started on jump leads, the problem isn't solved. Have the battery and charging checked soon, before you're stuck in a car park again. If it won't start even on jump leads, see what to ask when you call a tow.

What to do with the old battery#

A car battery contains lead and acid, so don't put it in the household bin or leave it behind the block. Hand it in at the garage or shop where you buy the new one, or at a hazardous waste collection point; ask beforehand where they take it. Carry it upright so no acid leaks out.

How CariX helps#

In the free driver account you add your car and keep what you need close at hand when it won't start.

• Roadside assistance on the car page: add the assistance number from your RCA (compulsory third-party insurance) or CASCO (comprehensive cover) policy and it's one tap away when the car won't start.
• Your own reminders: set a reminder yourself, for example for a battery test before winter, and get it by email.
• Active warranties: if the garage records the battery's warranty on the job line, you see it on the car and get an email reminder 30 days before it ends (for a warranty in months).
• "Is the price fair?" shows an indicative range for a battery replacement in your city, based on the prices businesses show in CariX; the real price depends on the car and the battery type.

See the other electrical services too, from air conditioning to wiring.