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Maintenance and tyres , On the road , Know your car · Updated 2026-10-18

Looking after your 12V car battery

Every car, including electric and hybrid ones, has a normal 12V battery. It starts the engine or wakes up the electronics, and it runs the lights, locks and computers. When it fails, the car simply does not start, often on the coldest morning of the year. A little care makes that much less likely.

How a car battery ages

A battery is a consumable part. It slowly loses capacity with age, with every deep discharge, and with heat. Cold does not damage it so much as expose weakness, because a cold battery delivers less power just when the engine needs more to turn over. Many batteries last several years, but there is no exact figure: use and climate matter a great deal.

What shortens battery life

• Many short trips: the alternator does not get time to recharge what the starter used.
• Leaving lights or electronics on: a deep discharge wears the battery down.
• Long periods standing: a parked car still draws a small current, and a battery left empty can be damaged.
• Heat: hot summers age batteries faster than people expect.
• Loose or corroded terminals: poor contact makes starting harder and charging worse.
• Added equipment: dash cameras, alarms and trackers wired to the battery can drain it.

Warning signs

• The engine turns over slowly, especially when cold.
• Headlights dim while cranking or at idle.
• The dashboard shows a battery or charging warning.
• Electronics reset themselves, or the stop-start system stops working.
• A swollen battery case or a smell of rotten eggs. Treat this as urgent and see a workshop.

If the battery warning light comes on while driving, the problem may be the charging system rather than the battery itself. See dashboard warning lights for what to do.

Simple care you can do

1. Look at the terminals now and then. White or green crust means corrosion; have it cleaned by a workshop if you are not comfortable doing it.
2. Make sure the battery is held firmly in place and the cables are tight.
3. Take a longer drive from time to time so the battery can recharge fully.
4. Switch off lights and accessories before you leave the car.
5. If the car will stand for weeks, ask the workshop about a suitable charger that maintains the battery safely.

Take care: a battery contains acid and can produce gas while charging. Do not use tools that could create a spark near it, and do not try to open it.

Get it tested before winter

The best time to find a weak battery is in autumn, not on a frosty morning. Most workshops and many tyre shops can test a battery in a few minutes. The test shows how much starting power remains, not just the voltage. If the result is poor, replacing it on your own schedule is cheaper and less stressful than a roadside call. Pair it with the other checks in winter preparation.

Replacing a battery

Use a battery with the capacity and type the car needs, as given in the manual. Cars with stop-start systems need a specific, stronger type. On many modern cars a new battery must be registered with the car's electronics, otherwise charging may not work as intended, so a workshop is often the safer choice. Make sure the old battery is recycled; the seller will normally take it back.

If the car will not start

A flat battery can be revived by a jump start, but there are steps that must be followed carefully. Read jump starting safely before you try, and if you are unsure, call for assistance. Modern cars with sensitive electronics can be damaged by a wrong connection.

Hybrids and electric cars

The high-voltage traction battery is a separate system and is not something an owner should touch. The 12V battery in these cars is still important, because without it the car may not "wake up" at all. Care for it the same way and have it tested at services.

Keep a record

Note the date a new battery was fitted. In My Garage you can store that date and set a reminder to test it before the next cold season.

What to remember

• The 12V battery is a wear item; age, heat and short trips shorten its life.
• Slow cranking, dim lights and a charging warning are signs to act.
• Have it tested in autumn, before the cold arrives.
• Check terminals and mounting; let a workshop handle anything unusual.
• Use the correct type, especially for stop-start cars.

Battery Beginner Checklist Do it yourself Service history Winter