Car Battery: When to Replace It and How to Choose the Right One

The battery is the part most often bought at the worst possible moment: after the car has failed to start, from the nearest shop, with no comparison. The result is that many people pay more than they should and end up with a battery that doesn't suit their car. This guide covers what to know before you reach that moment.

What has to match your car

A battery isn't one size. Three figures have to match what your car's manufacturer specifies:

• Capacity (amp-hours): below specification means weak starting and a shorter life; far above it adds little for the price.
• Cold cranking amps (CCA): determines the battery's ability to turn the engine in cold weather, and it's the figure whose effect shows in winter.
• Size and terminal orientation: it has to fit its tray and both cables must reach without strain. The simplest of the three and the most often overlooked in a rushed purchase.

The easiest method: photograph the old battery from above before going to buy — the label carries all three figures.

Signs a battery is near the end

The sign	What it means
Noticeably slow cranking	The clearest sign, and it appears first in the cold
Lights dimming on start-up	The battery isn't delivering enough current
Repeated need for a charge or a push	It no longer holds a charge
White or green corrosion around the terminals	Obstructing the connection — clean it before judging the battery
Swelling in the casing	Replace immediately

Check before you replace

Not every starting problem is a battery problem. Corroded terminals or a loose cable produce the same symptoms and are fixed by cleaning and tightening. And a failed alternator will consume a new battery within weeks — anyone replacing the battery without checking the charging system may buy it twice.

Before buying: clean the terminals, confirm both cables are tight, then have the battery and the alternator tested together.

When buying

• Check the manufacturing date — a battery loses capacity in storage even unused.
• Ask for an invoice stating the type and specification, and ask about the warranty, its length and what it covers.
• Inspect the casing: any swelling or cracking is reason to refuse it.
• Keep the old battery until you're satisfied the new one works.

Making a battery last

Two things shorten battery life most: leaving the car standing for long periods, and running electrics with the engine off. Frequent short journeys also give the alternator too little time to recharge. If your car stands for long stretches, run it periodically for a meaningful period rather than a few minutes.

For buyers

Browse the parts listings, and read how to spot counterfeit parts — batteries are among the parts where forgery shows up.

In short

Photograph your battery's label before you need a replacement, check the terminals and the alternator before replacing, and verify the manufacturing date and warranty when you buy.