How to replace a car battery

When to replace a starter battery

A starter battery is not replaced at a fixed point: it is replaced when it can no longer do its work, and a test shows that. As a rough guide, a starter battery often lasts four to six years. How long a particular battery lasts differs widely with the climate, the kind of journeys, the vehicle's electrical equipment and how the battery has been treated, so a battery can fail earlier or serve longer. Whether a battery has to be replaced is decided by the result of a battery test and by your vehicle manufacturer's service schedule, where it provides for testing or replacing the battery.

Have the battery tested when you notice one of these:

• The starter motor turns the engine more slowly than it used to, above all in cold weather or after the vehicle has been parked for a while
• The battery or charging warning comes on, or the vehicle shows a message about the battery or its state of charge
• The automatic start-stop system or other comfort functions are switched off by the vehicle more often than before
• The battery repeatedly needs charging or the engine repeatedly needs a jump start without an obvious reason such as lights left on
• The battery's case is swollen, cracked or leaking, or its terminals carry heavy deposits

A weak start is not proof of a worn battery. A battery that is merely discharged, loose or corroded terminal clamps, a poor earth connection, a fault in the charging system, a consumer that draws current while the vehicle is parked and a fault in the starter motor can cause the same signs, and a new battery does not cure these faults. Have the battery tested with a battery tester suited to its type, by a workshop or a parts dealer, and have the charging system and the current drawn by the parked vehicle checked as well if the battery fails early or goes flat repeatedly. A test that finds no fault does not rule one out: if the signs remain, have the vehicle checked by a workshop.

Do not charge, jump-start or go on using a battery whose case is swollen, cracked or leaking: such a battery can burst or release acid, and it has to be replaced. Do not charge or jump-start a battery that may be frozen either; have it thawed and checked as its maker's instructions describe, and replace it if it is damaged. Keep sparks and flames away from any such battery.

Before you start

A starter battery can give off a gas that explodes when a spark or a flame ignites it, and it contains acid that burns skin and eyes. It can also deliver a current that makes a metal tool or a ring dangerously hot if it bridges the two terminals, or the vehicle's body and the terminal that is not connected to the body, as a rule the positive one. Do not smoke, and keep flames, sparks and anything that glows away from the battery. Wear eye protection and acid-resistant gloves, take off rings, watches and bracelets, and never lay a tool on the battery.

• Obtain the vehicle manufacturer's procedure before you start: where the battery is and how it is reached, how long the vehicle has to stand with the ignition off before the battery is disconnected, the order of disconnecting and connecting, the tightening specifications for the terminal clamps and the battery's clamp, what has to be done after the battery has been connected, and whether a new battery has to be registered with the vehicle. If you cannot obtain it, or the job calls for equipment you do not have, leave the job to a workshop.
• Find the battery. On many vehicles it is in the engine compartment; on others it is in the luggage compartment, under a seat or under the floor, sometimes behind trim or under a cover. Parts that have to be removed for access are removed and refitted as the vehicle manufacturer describes.
• Find out whether your vehicle monitors its battery. Many vehicles, above all those with an automatic start-stop system, have a battery sensor on a terminal clamp, usually the negative one, and a control unit that manages charging. On such vehicles a new battery usually has to be registered with a diagnostic tool, and some vehicles require this for every battery change. If your vehicle requires it and you do not have a diagnostic tool that can do it for your vehicle, arrange for a workshop to do it before you start.
• Without a memory saver, disconnecting the battery interrupts the supply to the vehicle's control units. Depending on the vehicle, the clock, stored settings, the one-touch function of the windows and the sunroof, and an anti-theft code of the audio system can be lost, and some systems have to be set up again afterwards. Have any code that your audio system needs to hand before you disconnect anything, and read in the handbook what your vehicle needs after the battery has been disconnected.
• A memory saver may preserve some of the vehicle's stored settings through a diagnostic or accessory socket while the battery is out. Use one only if the vehicle manufacturer's instructions permit it, and follow its own instructions. While it is connected, the vehicle's cables stay live: each terminal clamp has to be insulated as soon as it has been disconnected, and the positive one must never touch the body or the negative one.
• Park the vehicle on level ground in a well-ventilated place with the parking brake applied. Switch off the ignition and every consumer, including the lights and the interior lighting, and keep the key or remote away from the vehicle, so that nothing switches on while you work. Keep the vehicle from locking itself with the key inside: leave a door open or a window lowered where that is needed. On vehicles whose door windows drop slightly when a door is opened, follow the handbook's instructions for opening and closing the doors while the battery is disconnected.
• Have the new battery ready before you remove the old one, and read the instructions supplied with it. Check that it is undamaged, and follow what those instructions say about charging before fitting: where they call for the state of charge to be checked, have a parts dealer or a workshop do that, and if they call for charging first, charge it with a charger suited to its type as they describe, in a ventilated place and not connected to the vehicle.
• A starter battery is heavy. Plan how you will lift it out and where you will set it down, and get help if its position makes lifting awkward. Keep it upright at all times.

Choose the right battery

Starter batteries differ in their capacity, the current they can deliver for a cold start, their dimensions, the kind and the position of their terminals, the rail at the bottom of the case by which they are clamped, their venting and their technology. A battery that fits into the tray is not therefore the right one: a battery of the wrong technology can fail early in a vehicle with an automatic start-stop system, terminals the wrong way round can leave the cables too short or lead to a connection with reversed polarity, and a battery that the clamp does not hold can move while driving. Fit only a battery listed for your vehicle.

Select your vehicle with the selector on this page to find the part numbers suppliers list for its engine. On the vehicle's part page, each part number is shown with the specifications its supplier states, such as the battery capacity, the cold start current, the length, the width and the height with terminal, the terminal post type, the pole configuration and the bottom rail version. Several of these are stated as the supplier's codes; if a code does not tell you what you need to know, ask the supplier.

• Technology: vehicles with an automatic start-stop system or with energy recovery are as a rule equipped with a battery built for frequent charging and discharging, and a battery of a simpler technology is not a substitute for it. Take the technology the vehicle manufacturer specifies for your vehicle. The specifications listed above do not always say which technology a battery has: check it in the supplier's own description of the part number.
• Capacity and cold start current: take the values the vehicle manufacturer specifies for your vehicle and its equipment. Where the manufacturer permits more than one, the vehicle's battery management may have to be told which is fitted, as described under After fitting.
• Dimensions and bottom rail: the battery has to stand flat in the tray and be held by the vehicle's clamp. Compare the length, the width, the height and the rail at the bottom of the case with the tray, the clamp and the space above the battery, including any cover.
• Terminals: the positive and the negative terminal have to be on the same sides and of the same kind as on the battery the vehicle was built for, so that each cable reaches its terminal without strain and each clamp fits its post.
• Venting: a battery fitted inside the vehicle's body, for example in the luggage compartment or under a seat, has to lead its gas outside through the vehicle's vent hose. Take a battery with a connection for that hose where your vehicle has one.
• Where more than one battery is listed for an engine, they can be equivalent parts from different suppliers or parts intended for different versions and equipment of the vehicle. Where a supplier states conditions for a part number, such as a production period or an equipment code, the vehicle's part page shows them with that part number: check them against your vehicle. If what is stated does not settle whether the battery fits, ask the supplier or the vehicle manufacturer before you buy.

Compare the new battery with the old one before you fit it, but do not take the old one as the specification: a battery that was fitted earlier may itself have been the wrong one. Choose a part number listed for your engine whose stated conditions match your vehicle and its equipment, and make sure that it meets the vehicle manufacturer's specification; a difference between the two batteries needs the supplier's or the vehicle manufacturer's confirmation.

All starter battery OE numbers in the catalogue

Disconnect and remove the old battery

1. Switch off the ignition and every consumer, keep the key or remote away from the vehicle, and let the vehicle stand for as long as the vehicle manufacturer's procedure requires before the battery is disconnected, so that its control units have shut down. If the engine has been running, let hot parts near the battery cool until you can work beside them without burns.
2. Gain access to the battery as the vehicle manufacturer describes. Where the bonnet or the tailgate has to be open, make sure that its stay or struts hold it securely. Remove any cover, heat shield or insulating jacket of the battery after releasing any clip or fastening, and keep these parts and their fixings together: they are fitted again later.
3. Identify the two terminals with certainty by the markings on the battery's case, not by the colour of the cables or the covers alone: the positive terminal is marked with a plus sign, the negative one with a minus sign. Note how the cables, any battery sensor and any vent hose are routed and fastened.
4. If you use a memory saver, connect it now as its instructions and the vehicle manufacturer's instructions describe, and treat both of the vehicle's battery cables as live from here on.
5. Disconnect first the terminal clamp that the vehicle manufacturer's procedure names first. On a vehicle whose body is connected to the battery's negative terminal, as on almost all current cars, that is the negative clamp. Loosen its nut or release its lever only as far as needed, and lift the clamp off the post by hand without levering against the battery's case or the post. If the clamp carries a battery sensor, handle the clamp as the vehicle manufacturer describes, do not pull or twist the sensor or its lead, and unplug its connector only if the procedure calls for it, after releasing any lock.
6. Cover the disconnected clamp with an insulating cover as soon as it is off the post. Then move its cable away from the battery and secure it so that it cannot spring back onto the post.
7. Disconnect the other terminal clamp, on such a vehicle the positive one, in the same way, after opening any cover over it and detaching any additional lead or fuse carrier from the clamp or the post as the vehicle manufacturer describes. Do not let the tool touch the vehicle's body or any metal part while it is on the positive clamp. Cover the positive clamp with an insulating cover as soon as it is off the post, keep any bare metal of the leads detached from it clear of the body, and secure the cable away from the battery.
8. If the battery has a vent hose, pull it off the battery's vent connection without kinking it. If an angled connector sits in the battery's vent opening, find out whether it belongs to the vehicle's hose or to the battery, and keep it if it belongs to the vehicle.
9. Remove the battery's clamp: depending on the vehicle, a clamp at the foot of the battery that grips the bottom rail, or a bracket or strap across its top. Undo its fixing with a tool that fits and keep the clamp and the fixing together. Do not drop a tool or a fixing onto the battery or beside it.
10. Lift the battery out upright, by its handle if it has one that is sound, otherwise with both hands under the case, and without tilting it. Do not lift it by its terminals. Set it down upright on a surface that acid cannot damage, away from sparks, flames and heat.
11. Look at the tray, the clamp, the terminal clamps and the cables. Remove deposits from the terminal clamps with the terminal brush and wipe the tray and the clamp with a cloth moistened with clean water, wearing the gloves and the eye protection; do not touch your face while you do so, and dispose of the cloth afterwards. Dry the tray. Remove anything that has fallen into it.

If a terminal clamp is cracked, deformed or no longer tightens on its post, if a cable is frayed, swollen or stiff with corrosion under its insulation, or if the tray or the clamp is corroded through, do not fit the new battery onto it. Have the damaged part replaced first.

Fit and connect the new battery

1. Check the new battery against the part number listed for the vehicle and compare it with the old one, as described under Choose the right battery: the dimensions, the bottom rail, the kind of terminals and which side each is on, and the vent connection. Do not fit a battery that differs until the difference has been cleared up, and do not fit one that is damaged or leaking.
2. Prepare the battery as its instructions describe. Take off the protective caps of its terminals only when you are ready to connect it. Where the battery has a vent opening on each side, fit the vehicle's vent hose or its angled connector to the opening the vehicle's hose reaches, and close the other opening with the plug supplied, if the battery's instructions call for that. Leave any plug or seal in place that the instructions do not tell you to remove.
3. Lift the battery into the tray upright and the right way round, so that each terminal is on the side of its cable. Make sure that it stands flat, that nothing lies under it, and that no cable or hose is trapped beside or beneath it.
4. Fit the battery's clamp so that it grips the bottom rail or holds the top of the case as the vehicle's design provides, and tighten its fixing according to the vehicle manufacturer's specification, with a torque wrench where a tightening value is given. The battery must not be able to move in any direction. Do not tighten further than specified: a clamp that is overtightened can crack the case.
5. Connect the vent hose to the battery's vent connection if the vehicle has one, and check that it is not kinked or trapped and that its other end is still in its outlet.
6. Connect the clamps in the order the vehicle manufacturer's procedure gives: on a vehicle whose body is connected to the battery's negative terminal, the positive clamp first and the negative clamp last. Take the protective cap off the positive terminal and the insulating cover off the positive clamp. Check that the clamp and the post are clean, dry and bright where they meet. Push the positive clamp fully down onto the positive post by hand; do not drive it on with a tool. Tighten it according to the vehicle manufacturer's specification, refit any additional lead or fuse carrier as the manufacturer describes, and close the cover over the positive terminal.
7. Before you connect the second clamp, on such a vehicle the negative one, check once more that it is the clamp for the post in front of it: the negative clamp belongs on the post marked with a minus sign. Then connect it in the same way: on the post fully, tightened according to the specification, with any battery sensor and its connector fitted and locked as the vehicle manufacturer describes. A small spark as the second clamp touches its post can occur when control units take up their supply; heavy sparking means that something is wrong: stop, do not go on connecting, and have a workshop find the cause.
8. Check that neither clamp can be turned or lifted on its post by hand, that both cables lie as they did before without strain, and that the positive cable and its clamp are clear of the body, the bonnet and the battery's clamp.
9. Apply a terminal protection product to the terminals only if the vehicle manufacturer's or the battery maker's instructions provide for it, and then only the product and in the way they describe. Keep it away from a battery sensor unless those instructions say otherwise.
10. Refit the cover, the heat shield or the insulating jacket of the battery and every part removed for access, with their fixings, as the vehicle manufacturer describes. If you used a memory saver, disconnect it as its instructions describe. Remove all tools, cloths and insulating covers from the area of the battery and account for each of them before you close the bonnet, the tailgate or the trim.

Connecting a battery with reversed polarity, however briefly, can destroy fuses, the alternator and control units and can start a fire. If you are not certain which terminal is which, stop and do not connect anything.

After fitting

1. Where the vehicle requires a new battery to be registered, register it with the diagnostic tool as the vehicle manufacturer's procedure describes, with the details of the new battery that the procedure asks for, or have a workshop do it without delay. Until it is done, the vehicle can charge the new battery as if it were the old one, which can shorten its life, and functions such as the automatic start-stop system can stay switched off.
2. Switch on the ignition and see which warnings remain lit. Carry out what the handbook and the vehicle manufacturer's procedure require after the battery has been disconnected: depending on the vehicle, setting the clock, entering the audio system's code, setting up the one-touch function of the windows and the sunroof again, and steps for the steering, the stability control or the engine's idle control.
3. Start the engine only in the open air, with the parking brake applied and the transmission in neutral or in the park position, and with hands, clothing, tools and cloths clear of belts, pulleys and fans. Check that the engine starts normally and that the battery or charging warning goes out.
4. Some warnings go out only once the vehicle has been driven, where the vehicle manufacturer's information says so. If a warning stays on that the handbook does not explain in this way, or if the battery or charging warning stays on with the engine running, switch off the engine and have the vehicle checked by a workshop before you rely on it.
5. An automatic start-stop system can stay inactive for some time after a battery change, until the vehicle has assessed the new battery. If it does not return, or the vehicle reports a battery fault, have the registration and the battery sensor checked.
6. Hand in the old battery where you bought the new one or at a collection point for old batteries. Carry it upright, with its terminals covered, secured so that it cannot tip over, and in a tray or container that holds any acid that escapes. An old battery is hazardous waste and does not belong in household waste; in many countries a deposit is charged on a new battery until an old one is returned.

Mistakes to avoid

• Disconnecting or connecting the terminal clamps in another order than the vehicle manufacturer's procedure gives: on a vehicle whose body is connected to the negative terminal, the positive clamp first off or the negative clamp first on
• Letting a tool touch the positive terminal and the vehicle's body at the same time, or laying a tool on the battery
• Smoking or causing sparks beside a battery
• Connecting the battery with reversed polarity
• Fitting a battery of a simpler technology in a vehicle that requires a battery built for start-stop operation
• Fitting a battery whose terminals are on the wrong sides and stretching the cables to reach them
• Leaving the battery loose in its tray, or overtightening its clamp
• Driving a terminal clamp onto its post with a tool, or leaving a clamp loose
• Leaving the vent hose off a battery that is fitted inside the vehicle's body
• Pulling or twisting a battery sensor or its lead
• Not registering the new battery on a vehicle that requires it
• Using a memory saver where the vehicle manufacturer does not permit it, or leaving the live clamps uninsulated while it is connected
• Tilting an old battery, or putting it in household waste