Car Battery Maintenance: How to Make Yours Last Longer

A car battery gives very little warning before it fails, and when it does, it usually does so on the coldest morning of the year with somewhere important to be. The good news is that most of the maintenance that extends battery life takes minutes and costs nothing.

How do you maintain a car battery?

Regular battery maintenance comes down to five things: keep the terminals clean and tight, keep the battery clamped down, keep it charged by driving the car properly or using a maintainer, avoid draining it with the engine off, and check the resting voltage occasionally so you find a weak battery before it strands you.

A practical routine:

• Look at it every few months. Open the bonnet, or the boot on cars where the battery lives there, and check for white or blue crusty deposits on the terminals, a cracked case, a swollen case or any sign of leakage.
• Clean the terminals when corrosion appears rather than waiting for a starting problem.
• Check the clamp. The battery should not move at all in its tray. Vibration destroys the internal plates and loosens connections.
• Test the voltage with a cheap multimeter once or twice a year, and before winter in particular.
• Give it a proper run if the car does mainly short journeys, or fit a maintainer.
• Switch everything off before you leave the car, including interior lights, and check the boot light actually goes out.

How long does a car battery last?

Most car batteries last three to five years in normal UK use. Some reach seven, and plenty die at two. The variation is almost entirely down to how the car is used rather than the brand on the label.

What shortens battery life:

• Short journeys. A five minute trip uses more charge starting the engine than the alternator puts back, so the battery slowly discharges over weeks.
• Long periods standing. Every modern car draws a small current when parked to keep alarms, telematics and control modules alive.
• Heat. Sustained high temperatures evaporate electrolyte and corrode the internal plates. Heat does the damage, and cold weather exposes it.
• Deep discharges. Every time a battery is run completely flat it loses some capacity permanently. Three or four flat batteries and it will never be reliable again.
• Vibration from a loose clamp or a rough road.

What are the signs of a failing car battery?

The earliest reliable sign is a slower crank when starting, particularly first thing on a cold morning. The starter sounds laboured rather than crisp, and the engine takes a fraction longer to fire than it used to.

Other symptoms worth acting on:

• Headlights and interior lights dimming noticeably at idle, or brightening as you rev the engine.
• The battery or charging warning light on the dashboard. That symbol indicates a charging system fault as well as a battery fault, so it needs diagnosing rather than assuming a new battery is the answer.
• Electrical oddities, such as the radio resetting, the central locking behaving inconsistently or a stop start system that stops working. Stop start switching itself off is often the very first sign, because the car will not shut the engine down if it doubts the battery can restart it.
• A swollen or misshapen case, which means the battery has been overcharged or cooked and needs replacing regardless of whether it still starts the car.
• The smell of rotten eggs near the battery, which indicates it is venting and should be replaced without delay.

How do you test a car battery with a multimeter?

Set a multimeter to 20V DC, touch the red probe to the positive terminal and the black probe to the negative, and read the voltage with the engine off and the car having stood for at least an hour. A rested, fully charged battery reads around 12.6 to 12.8 volts.

Then start the engine and measure again. With the engine running you should see roughly 13.7 to 14.7 volts, which shows the alternator is charging. A reading that stays at battery voltage means the charging system is not working. A reading well above 15 volts suggests a regulator fault, which will boil the battery dry.

A voltage test tells you the state of charge but not the battery's true health. A battery can read 12.6 volts and still collapse under the load of the starter motor. Any garage can carry out a load or conductance test in a couple of minutes, and that is the test that gives a definite answer.

How do you clean corroded battery terminals?

Disconnect the negative lead first, then the positive, scrub the corrosion off with a wire brush and a solution of bicarbonate of soda and warm water, rinse carefully, dry thoroughly, then reconnect the positive first and the negative last.

Points that matter:

• Order is not optional. Negative off first and negative on last means that if your spanner touches bodywork while you are working, nothing shorts.
• Wear eye protection and gloves. The deposits are acidic and the electrolyte inside is sulphuric acid.
• Neutralise the corrosion. Bicarbonate of soda and water neutralises acid residue. Keep the solution out of the vent caps and off the paintwork.
• Dry everything properly before reconnecting, and smear a thin film of petroleum jelly or proper terminal grease on the posts afterwards to keep moisture out.
• Check the clamps are tight but not overtightened. Lead terminals distort easily.
• Look at why it corroded. Heavy build up on the positive terminal in particular can be a sign of overcharging.

Battery acid on paintwork does real damage. If any electrolyte has spilled onto the inner wing or bonnet, rinse it off with plenty of water immediately, because it will etch through the lacquer and start corrosion underneath. Damage that has already eaten into the paint needs stripping back and refinishing rather than polishing.

How do you jump start a car safely?

Connect red to the flat battery's positive terminal, red to the donor battery's positive, black to the donor battery's negative, and the final black clamp to a clean unpainted metal earth point on the flat car, away from the battery. Start the donor car, let it run for a few minutes, then try the flat car.

The reason the last clamp goes on bodywork rather than the flat battery's negative post is that the final connection sparks, and a discharged battery gives off hydrogen. Keeping that spark away from the battery is basic safety, and it is the step most people skip.

The full procedure:

• Park the cars close but not touching. Handbrakes on, both ignitions off.
• Check the flat battery is not cracked, leaking or frozen. Never jump start a damaged or frozen battery.
• Connect the four clamps in the order above, keeping the leads away from belts and fans.
• Start the donor car and run it for three to five minutes.
• Try the flat car. If it does not start within a few seconds of cranking, stop and wait rather than grinding the starter.
• Once running, remove the clamps in exactly the reverse order.
• Drive for at least half an hour, ideally at steady road speeds rather than idling, to put some charge back.

Two cautions. First, some manufacturers specify particular jump points and advise against connecting directly to the battery at all, so check the handbook, particularly on cars where the battery lives in the boot and there is a dedicated terminal under the bonnet. Second, a portable lithium jump pack is safer, cheaper and far more convenient than relying on a stranger's car, and it removes any risk to the donor vehicle's electronics.

If the car needs jump starting more than once, the battery is not the only thing that needs looking at. Get the charging system and the parasitic drain checked.

Why do car batteries fail in winter?

Cold weather does not usually cause the failure, it exposes a battery that was already weak. Chemical reactions inside the battery slow as the temperature drops, so available cranking power falls at exactly the moment the engine needs more of it, because cold oil is thicker and harder to turn.

Add the extra load of heated screens, heated seats, lights, wipers and blowers on a short dark commute, and a battery that coped all summer runs out of margin in December. This is why a voltage check in October is worth far more than one in June.

Practical winter measures:

• Have the battery load tested before winter if it is more than three years old.
• Let the engine start before switching on heated screens and blowers, and turn them off before you shut the engine down.
• If the car is used rarely, fit a smart maintainer. Modern chargers can be left connected indefinitely and simply top the battery up as needed.
• Keep the battery terminals clean, because a poor connection has more impact when the battery is already working hard.

Flooded, EFB or AGM: which battery does your car need?

Fit the type the vehicle was designed for. A stop start car with an AGM battery must have an AGM replacement, because the charging strategy and the number of engine restarts will destroy a standard flooded battery in months.

When choosing a replacement, match four things: the physical case size and hold down type, the terminal layout and which side the positive post is on, the capacity in amp hours, and the cold cranking amps rating. Fitting a battery with a lower cold cranking figure than the manufacturer specified is a false economy in a British winter.

Batteries with removable caps can have their electrolyte level checked, and topped up with distilled or deionised water only. Tap water contains minerals that contaminate the plates. Most modern batteries are sealed and have no serviceable fluid level at all, so if there are no caps, leave it alone.

How do you dispose of an old car battery in the UK?

Take it to a household waste recycling centre, a scrap metal dealer or the retailer you bought the replacement from. Lead acid batteries are classed as hazardous waste and must never go in a household bin, and most retailers that sell batteries will take the old one back.

Transport it upright, ideally in a plastic tray or box, and do not tip it on its side. Lead is one of the most efficiently recycled materials there is, and the acid is neutralised and processed rather than discarded.

When is it worth getting professional help?

Get a garage involved when the battery is repeatedly going flat, when the charging warning light is on, when you suspect a parasitic drain, or when the car needs the new battery registering to its battery monitoring system. Those jobs need a multimeter used properly, a current clamp and often a diagnostic tool, and guesswork gets expensive.

Battery acid, spilled electrolyte or a long standing leak can leave etched, blistered paint on the inner wing and slam panel that only shows up once the battery comes out. If you find corrosion or damaged paint under a battery tray, our vehicle body repairs team at Radcliffe can assess it, and for anyone handing a leased vehicle back, our lease car repairs service covers the cosmetic work before the inspection.