How to check a car battery: a guide to charging and jump starting

Because nothing kills your day faster than a car that just… clicks.

There are few sounds more deflating than turning the key (or pressing the button) and being greeted by silence. Or worse, a weak, half-hearted cough that says, “I’m not doing this today.”

If the engine is the heart of your car, the battery is the lungs. No battery, no breath. No lights, no infotainment, no heated seats, no electronic handbrake—and definitely no going anywhere.

The good news? Checking your car battery isn’t witchcraft. You don’t need to be an electrician or own a garage full of tools. With a bit of know-how, you can spot trouble early, keep it charged, and avoid the classic cold-morning breakdown outside your own house.

Let’s get into it.

What actually is a car battery?

At its simplest, a car battery is a big rechargeable power pack. It stores electricity and releases it when needed—mainly to start the engine, but also to power everything from your headlights to your climate control.

Most petrol and diesel cars use lead-acid batteries, while electric cars use large lithium-ion batteries for driving and still have a smaller 12V battery for accessories. Yes, even EVs can suffer a flat battery. Cruel irony.

Battery size and type vary depending on the car, especially if it has start-stop technology, which demands more from the battery and usually requires a specific AGM or EFB type.

How to check your car battery (no tools required)

Before you go anywhere near chargers or cables, start with the basics.

1. How does the car start?

If the engine:

• Takes longer than usual to fire

• Sounds laboured or sluggish

• Needs a second attempt

That’s often your first clue the battery is running low.

2. Check the headlights

With the ignition on and engine off, turn on the headlights.

• Bright and steady? Good sign

• Dim or fading? Battery could be struggling

(LED headlights are more efficient, so this test isn’t always conclusive—but it’s still worth doing.)

3. Look for the battery health indicator

Many batteries have a small coloured window on top:

• Green = healthy

• Red = low charge

• Clear or black = likely flat

Not all batteries have one, but if yours does, it’s a handy quick check.

Checking a car battery with a multimeter

A multimeter sounds intimidating. It isn’t. And decent ones cost less than a takeaway.

How to do it:

1. Set the multimeter to DC voltage (V with a straight and dashed line)

2. Touch the red probe to the positive terminal (+)

3. Touch the black probe to the negative terminal (–)

What you’re looking for:

• 12.6V or higher = healthy

• 12.2–12.4V = partially discharged

• Below 12V = needs charging

If the number’s low, don’t ignore it. Batteries rarely heal themselves.

How to charge a car battery

If your car is slow to start but otherwise fine, charging the battery can bring it back to life.

A smart battery charger is the easiest option. Modern ones monitor the battery and adjust the charge automatically. The NOCO range is a popular choice for exactly this reason.

Charging basics (no panic required)

• Locate the battery (bonnet, boot, or under a seat)

• Connect red clamp to +, black clamp to –

• Select the correct mode on the charger

• Plug it into the mains and let it work

Charging can take several hours, so this is very much an overnight job, not a lunch-break one.

When finished:

• Switch off at the mains

• Disconnect clamps

• Replace covers

If the car still won’t start afterwards, the battery may be at the end of its life.

How to use a jump starter (modern lifesaver)

Forget jump leads and awkward conversations with strangers. Jump starters are compact, powerful, and brilliantly simple.

Think of them as a battery in a box.

How they work:

1. Connect clamps to the battery terminals

2. Turn the car on

3. Disconnect the jump starter

4. Drive away like nothing happened

Some even double as torches, power banks, or tyre inflators. Handy stuff. The Clarke jump packs are a solid example of the type.

Just remember to recharge the jump starter when you get home—otherwise it’s just decorative luggage.

How to avoid a flat battery in the first place

A few habits make a big difference:

• Drive the car regularly

• Avoid constant short trips

• Take longer runs so the alternator can recharge properly

• Use a trickle charger if the car sits unused

Starting the engine uses a huge amount of power. If you only ever drive five minutes to the shop, the battery never fully recovers.

Why car batteries fail in winter

Cold weather is brutal on batteries.

• Chemical reactions slow down

• Engines need more power to start

• Lights, heaters, and screens work harder

Add lots of short journeys into the mix and winter becomes the perfect storm for battery failure. If your battery is already on the way out, winter will expose it—fast.

Final thought: boring component, massive impact

Car batteries aren’t exciting. No one brags about them. But when they fail, they fail loudly—and inconveniently.

A quick check now, a charger in the garage, or a jump starter in the boot can save you time, money, and that awkward call for help when you’re already late.

Your car doesn’t ask much. Just make sure it can breathe.