DIY GUIDE · VEHICLES & TRANSPORT

How to change a car battery yourself
Half an hour on an older car. £68–£225 for the battery and terminal parts.

Glasses on, earth off first, positive on first, earth on last — and check whether your car needs the battery registered.

DIFFICULTY
Easy
part of the job only
TIME
Half an hour
ten minutes to identify the right battery, twenty to swap it, longer if it lives under a seat or in the boot
MATERIALS
£68–£225
a new battery — conventional at the low end, AGM for start-stop at the high end — and a terminal connector
A PRO CHARGES
£100–£400
typically £235
  • Every step, start to finish
  • Checked October 2026 — sources at the end
  • Honest about when to call a pro

FIRST, THE HONEST ANSWER

Do it yourself, or get a garage?

Do it yourself if…

  • The car is an older petrol or diesel without start-stop, or the handbook says the battery is self-learning
  • The battery is easy to reach under the bonnet or in the boot
  • You have the radio code and know how to reset windows and the clock if they lose their memory
  • You can lift a heavy battery out of its tray without twisting your back

Get a pro if…

  • The car has start-stop or an advanced energy management system that needs the battery registered or coded
  • It is a hybrid or electric car, where the high-voltage system must not be touched
  • The battery is hidden under a seat, behind trim or needs other parts removed to reach it
  • The battery tray shows heavy corrosion from leaked acid, which needs investigating

Safety first

  • Wear safety glasses and gloves throughout. Batteries contain sulphuric acid, and the safety regulator's guidance on vehicle maintenance calls for protective equipment when handling battery acid.
  • Never let a spanner bridge the positive terminal and the car body. Remove the earth (negative) lead first and refit it last, so a slip on the positive side cannot cause a short circuit — the battery maker gives this order for exactly that reason.
  • Work in a well-ventilated place with no flames, cigarettes or sparks nearby. Batteries give off explosive gas, especially while charging, and the safety regulator warns of explosion from battery gases.
  • On a hybrid or electric car, never touch anything with orange cabling. The safety regulator says these systems run at up to 650 V dc and that contact above 110 V dc can be fatal.
  • Lift the battery with both hands, close to your body, with your knees bent, and set it down upright. Never carry it by its terminals.
  • Keep metal jewellery off your hands. A ring or watch strap across the terminals heats up instantly.

Stop here: Stop here: battery registration, high-voltage systems and warning lights

Many cars with start-stop or an advanced energy management system need the new battery registered with a diagnostic tool, sometimes with a code specific to the battery; the battery maker we looked at warns that if it is not done correctly the start-stop and comfort functions can be restricted or fail. On hybrid and electric cars, the safety regulator warns that the high-voltage system — up to 650 V dc, usually with orange cables — can deliver a fatal electric shock and can retain dangerous voltage when switched off, and that work on it needs specific training. A warning light that stays on after the swap, especially the airbag light, needs a diagnostic check. Swapping a 12V battery on a car that does not need registering is the householder's part; the rest is not. How to hire a car battery fitter →

MATERIALCOVERAGEFOR THIS JOB
New batterySame size, layout and technology; same or higher capacityOne
Terminal connector, if a clamp is damagedPositive or negative to suitOne, only if needed
Terminal protection grease or sprayA thin coat after tighteningA little

Is the old battery really flat?

Resting voltage after the car has stood for a few hours: about 12.8 V means charged; below 12.4 V means recharge it; a battery that will not hold its charge after a full recharge needs replacing. Example: 12.1 V overnight, charged to 12.8 V, back to 12.2 V the next morning — replace it.

Start-stop batteries need a state-of-health test, not just a voltage reading.

Size, terminal layout and hold-down

The battery must fit the tray, hold-down and cable reach. Note the old battery's dimensions, which side the positive terminal is on, and how it is clamped down, or use a battery finder with your registration. The maker we looked at notes the tray is usually built to take more than one size.

Conventional, EFB or AGM

A car with start-stop needs a start-stop battery — enhanced flooded (EFB) or absorbent glass mat (AGM) — because a conventional battery is not built for the constant cycling. Replace like for like or better, and never fit a conventional battery where an EFB or AGM was fitted. The maker is blunt: never downsize.

Cold cranking and capacity

Two numbers on the label matter. The cold start current is measured to a standard test, EN 50342-1, at -18°C and governs winter starting. The capacity in Ah tells you how much charge the battery holds; the maker says a small car may need 40–45 Ah and premium cars up to 110 Ah. Match or exceed the original.

Voltage

Almost every modern car uses a 12V battery. Some vintage cars need 6V, and fitting a 12V battery to them would destroy the electrics. Check before you buy if the car is old.

Does your car need registering?

Cars with an energy management system monitor the battery's age and adjust charging to suit. The maker we looked at describes two groups: self-learning systems that adapt on their own over time, and systems that need the new battery registered with a diagnostic tool, sometimes with a battery-specific code. Check the handbook or ask a dealer before you buy; it decides whether this is a DIY job.

Have the radio security code, the locking wheel nut key and any reset instructions ready before you disconnect anything.
Most retailers take your old battery back when you buy a new one — ask when you buy.

THE PART THAT DECIDES THE FINISH

Before you start — by where your battery is

The swap itself is the same everywhere; what changes is getting to the battery and what the car does when it loses power. Find your car below and do its list first.

Under the bonnet, on an older car

The simple case.

  1. Park on level ground, handbrake on, engine off and key out of the car
  2. Note which side the positive terminal is, and photograph the cable routing
  3. Find the radio code, and make sure you can reset the clock and windows afterwards
In the boot or under a seat

Common on newer and larger cars.

  1. Lift the boot floor or seat cover and check for a vent tube from the battery to the outside; it must be refitted
  2. Check there is room to lift the battery straight up without tilting it
  3. Some cars have a remote positive terminal under the bonnet; read the handbook so you know which terminal to use
A car with start-stop

Check before you buy.

  1. Read the handbook for battery replacement instructions, or ask a dealer whether the battery must be registered
  2. Buy the same technology — EFB or AGM — and the same or larger capacity
  3. If registration is needed and you have no suitable diagnostic tool, this is where the job stops
A hybrid or electric car

Only the 12V battery, if at all.

  1. Find the 12V auxiliary battery from the handbook; it is separate from the high-voltage battery
  2. Keep well clear of orange high-voltage cables and anything labelled high voltage
  3. If the 12V battery is not easy to reach without disturbing other components, have it done by a garage
A flat battery you suspect is dead

Check before you replace.

  1. Test the resting voltage with a multimeter: the maker we looked at gives about 12.8 V for a healthy charged battery and says to recharge below 12.4 V
  2. Charge it fully and test again before condemning it
  3. Start-stop batteries need a proper tester for their state of health; a voltage check is not enough

THE JOB

How to change a car battery

  1. Get ready and find the battery

    10 min

    Park on level ground, apply the handbrake, switch everything off and take the key out of the car. Put on glasses and gloves. Find the battery from the handbook and go to the section above for where yours is. Photograph the terminals and cable routing so you can put it all back exactly.

    • Have the radio code and the new battery to hand before you start
    • Take off any rings or watch
    • Check the new battery's terminals are on the same sides as the old

    Mistake to avoid: Starting with the key in the car. Some cars lock themselves when the power comes back, with the key inside.

  2. Disconnect the earth lead

    5 min

    Loosen the clamp on the negative terminal, marked minus and usually with a black cable to the body, and lift it off. Tuck the cable well away from the battery so it cannot spring back onto the terminal. This is always the first lead off.

    • Negative first, every time
    • Wrap the clamp in a rag so it cannot touch the terminal
    • Do not let the spanner touch anything else while you work

    Mistake to avoid: Taking the positive off first. If the spanner touches the body while it is on the positive terminal, you short the battery through the tool.

  3. Disconnect the positive lead

    5 min

    Lift the plastic cover, loosen the clamp on the positive terminal, marked plus and usually red, and lift it off. Keep it clear of the battery and the body.

    • Loosen the clamp enough to lift straight off; do not twist the terminal
    • Check for a second, smaller cable on the positive and note where it goes
    • Keep the cover safe; it stops shorts

    Mistake to avoid: Prising a stuck clamp off by levering against the battery. Twisting stresses the terminal post and can crack the case.

  4. Release the hold-down and lift the battery out

    5 min

    Undo the clamp or bar that holds the battery in its tray and put it somewhere safe with its bolts. Disconnect any vent tube. Lift the battery out with both hands, upright, close to your body and with knees bent, and stand it on the ground.

    • Keep the battery upright at all times
    • Use the carry handle if it has one
    • Put it on a piece of card in case of acid residue

    Mistake to avoid: Lifting with a twist from an awkward position. A battery is heavy, and the back injury happens on the lift, not the carry.

  5. Clean and check the tray and clamps

    5 min

    Inspect the tray and hold-down for corrosion and damage, as the maker we looked at advises. Wipe away any white or green deposits with a rag and a little water with baking soda, then dry it. Clean the inside of both cable clamps with a wire brush until they are bright metal.

    • Heavy corrosion in the tray can mean the old battery leaked; have that checked
    • Bright, clean clamps make the best contact
    • Replace a cracked or badly corroded clamp

    Mistake to avoid: Fitting a new battery into dirty clamps. Corrosion adds resistance, and the new battery can seem weak or fail early.

  6. Fit the new battery

    5 min

    Lower the new battery into the tray with the terminals the same way round as the old one. Remove any transport caps or bungs as its instructions say, reconnect the vent tube if there is one, and refit the hold-down so the battery cannot move.

    • Check the positive terminal is on the same side as the positive cable
    • The hold-down must stop all movement; vibration shortens battery life
    • Do not overtighten the hold-down onto the case

    Mistake to avoid: Leaving the battery loose in the tray. It moves on every corner, the terminals work loose, and the case can be damaged.

  7. Connect the positive lead

    5 min

    Check the polarity once more. Fit the red positive clamp onto the positive terminal, push it fully down, and tighten it to the torque in the vehicle manual. Refit the positive cover.

    • Positive goes on first
    • Push the clamp fully down the post before tightening
    • Use a torque wrench if you have one; over-tightening cracks clamps

    Mistake to avoid: Connecting the earth first. With the earth already on, any slip of the spanner on the positive terminal touching the body causes a short.

  8. Connect the earth lead

    5 min

    Fit the black earth clamp onto the negative terminal last and tighten it to the same torque. A small spark as it touches is normal. Check both clamps cannot be twisted by hand, and apply a thin coat of terminal protection.

    • Earth on last, always
    • Check both clamps are tight and the covers are back on
    • Wipe away any grease that has strayed onto the case

    Mistake to avoid: Leaving a clamp finger-tight. A loose clamp makes intermittent contact and can make the car's electronics behave oddly.

  9. Start, reset and check

    10 min

    Start the engine and check the warning lights go out. Enter the radio code, set the clock, and reset the one-touch windows and anything else the handbook lists. The maker we looked at notes some cars need systems such as sensors recalibrated after a battery change; if any warning light stays on, especially the airbag light, stop and have it checked.

    • Follow the handbook's reset steps for windows and sunroof
    • Let the engine run for a few minutes
    • Check the charge warning light goes out

    Mistake to avoid: Ignoring an airbag or other warning light that stays on. It means a system needs a reset or a fault check that a battery swap cannot fix.

  10. Return the old battery

    15 min

    Take the old battery back to the shop that sold you the new one, or to your council's household waste and recycling centre. Carry it upright in a box in the boot, wedged so it cannot tip.

    • Never put a car battery in a household bin
    • Ask the retailer about take-back when you buy
    • Check your council's limits before you go

    Mistake to avoid: Leaving the old battery in the garage for years. It can leak acid, and it is hazardous waste that must go to a proper collection point.

The mistakes that cause trouble

  • Removing the positive lead first, so a slipping spanner can short the battery
  • Fitting a conventional battery where the car needs EFB or AGM
  • Not registering the battery on a car that needs it, so the charging and start-stop misbehave
  • Leaving the battery loose in its tray or the clamps under-tightened
  • Throwing the old battery in a bin instead of returning it

Stop here and get a battery fitter

  • The car's handbook says the new battery must be registered or coded, and you have no suitable diagnostic tool
  • It is a hybrid or electric car and the 12V battery cannot be reached without going near orange high-voltage cabling
  • An airbag or other warning light stays on after the swap
  • The tray is badly corroded or the cables are damaged
How to hire a car battery fitter →

The car will not start after fitting the new batteryA clamp is loose or dirty, or the battery was discharged on the shelf. Check both clamps are clean and tight; test the voltage, and charge the battery if it is low.
The start-stop no longer worksThe battery has not been registered, or the system has not yet learned the new battery. Check the handbook; if registration is needed, have it done with a diagnostic tool.
The radio asks for a codeIt lost power and is locked. Enter the code from the handbook or the card in the service book; a dealer can supply it with proof of ownership.
The electric windows no longer go up in one touchThe window controllers forgot their end positions. Reset them as the handbook describes, usually by holding the switch up for a few seconds after the window closes.
A warning light is on that was not on beforeA system lost its settings or needs recalibrating. Some clear after a short drive; if the airbag light or a safety warning stays on, have it checked.
White or green crust on the terminalsCorrosion from acid vapour. Clean with a brush and a little water with baking soda, dry, and protect with terminal grease.
The new battery went flat again within daysA fault in the charging system or something draining power with the car off. Have the alternator and the parasitic drain checked.
A rotten-egg smell from the batteryThe battery is overcharging or damaged and giving off gas. Ventilate, keep sparks away, and have the charging system checked.

WHAT YOU SAVE

What it costs to do it yourself

New battery, conventional to AGM£66–£220
Terminal connector or adapters, if needed£1.69–£5.19
Total£68–£225
DIY total£68–£225
A car battery fitter charges per battery
LOW
£100
TYPICAL
£235
HIGH
£400
Car Battery Replacement price guide →

Guide prices compiled by the Locufy team from published Irish and UK provider price lists and 2026/27 cost guides. Updated 2026.

Battery prices from a national motoring retailer, from a conventional battery for an older small car to an AGM for start-stop. A fitted battery from the price guide is shown alongside; it includes the battery itself, so the saving is the labour and the registration.

RATHER NOT?

Car battery fitters near you, with prices shown

The ones who cover your area, nearest first, with one score from every review. No account needed to look.

Or post the job free and let them come to you.

Return the old battery properly

Car batteries are hazardous waste and must not go in household bins. Take it back to the retailer, or to your council's household waste and recycling centre: one council accepts up to two lead-acid batteries from a household every 6 months and refuses lithium-ion and damaged batteries, so check your own council's rules. Battery producers must also collect waste car batteries free of charge on request.

Check the terminals after a week

Make sure the clamps are still tight and there is no corrosion. Retighten to the torque in the handbook if needed.

Keep the battery charged

If the car is used only for short trips or stands for weeks, a smart charger or maintainer keeps the new battery healthy. The maker we looked at suggests charging every two months for cars used only now and then.

Keep the paperwork

Keep the receipt and guarantee with the car's papers. A guarantee claim usually needs proof of purchase.

Changing a car battery: questions people ask

The negative, or earth, first; then the positive. When fitting, connect the positive first and the negative last. That order stops a spanner shorting the positive terminal to the car's body.

On many cars with start-stop or an advanced energy management system, yes. The battery maker we looked at describes some systems as self-learning and others as needing registration with a diagnostic tool. Your handbook or a dealer can tell you which your car has.

No. A start-stop car needs an EFB or AGM battery built for constant cycling, and you should replace like for like or better. A conventional battery fails quickly in a start-stop car.

Test the resting voltage with a multimeter after the car has stood. The maker we looked at gives about 12.8 V for a charged battery and says to recharge below 12.4 V. If it will not hold a charge after a full recharge, replace it.

Back to the retailer, or to your council's household waste and recycling centre. Car batteries are hazardous waste and must never go in a household bin.

The Locufy UK price guide puts a fitted car battery at £100–£400 per battery, typically £235 — the same three figures as the strip at the top of this page. That usually includes the battery and any registration.

MORE GUIDES

More DIY guides

Fitting a dash camFitting a car stereo and speakersValeting a carDetailing a carRepairing car paint scratches and chipsApplying a ceramic coating
All 90 DIY guides →How to hire a car battery fitter →Car Battery Replacement price guide →Car battery fitters on Locufy →

Sources — checked October 2026

  1. HSE — vehicle inspection, maintenance and repair: battery gases, short circuits, ventilated charging, protective equipment for acid
  2. HSE — electric and hybrid vehicles: up to 650 V dc, above 110 V dc can be fatal, orange cables
  3. VARTA Automotive — battery replacement step by step: earth cable first, red positive then black earth, torque from the vehicle manual, 58% under the bonnet, 40–45 Ah to 110 Ah, EN 50342-1 at -18°C
  4. VARTA Automotive — the right coding of the battery energy management system: self-learning versus registration with a diagnostic tool; never downsize
  5. VARTA Automotive — car battery testing: about 12.8 V charged, recharge below 12.4 V
  6. VARTA Automotive — FAQ: charge every two months if used sporadically, registration on advanced energy management
  7. Staffordshire County Council — car batteries at recycling centres: two lead-acid batteries every 6 months, no lithium-ion or damaged batteries
  8. Waste Batteries and Accumulators Regulations 2009, regulation 36 — producers must collect waste automotive batteries free of charge
  9. Halfords — car batteries price check: £66–£220
  10. Halfords — battery accessories price check: terminal connectors and adapters £1.69–£5.19