When an alternator fails, the car runs on battery power alone until the battery is flat, and then it stops, often somewhere inconvenient. The good news is that most alternator failures give some warning, and the repair is usually a few hundred pounds rather than thousands. Here's what an alternator replacement typically costs in the UK, how to spot the signs early, how to tell a failing alternator from a tired battery, and where a car warranty can help.
What does an alternator do?
The alternator is a small generator driven by the engine's auxiliary belt (often called the fan belt or serpentine belt). While the engine runs, it produces electricity to power everything from the headlights and wipers to the engine's own control units, and it recharges the battery at the same time.
The battery's main job is to start the engine. Once the car is running, the alternator takes over. If it stops charging, the car keeps going on whatever is left in the battery, which on a modern car packed with electronics might be anything from a few minutes to around an hour, depending on how much is switched on.
Modern alternators are more complex than they used to be. Cars with stop-start often use a heavier-duty or "smart" alternator that the engine computer controls to save fuel, and some premium and hybrid-style systems use a combined starter-generator. These tend to cost more to replace.
Signs your alternator is failing
Alternators rarely fail without warning. Watch out for:
- The battery warning light coming on while you're driving. Despite the symbol, this light usually means the charging system isn't working, and the alternator is the most common culprit.
- Dim or flickering headlights and dashboard lights, especially at idle, which brighten when you rev the engine.
- Electrical gremlins, such as slow electric windows, a radio that cuts out, or random warning messages on the dashboard.
- A whining or grinding noise from the front of the engine that rises with engine speed, often a worn alternator bearing.
- A burning smell, either hot wiring or a belt slipping on a seized pulley.
- A flat battery that keeps going flat, even after it has been charged or replaced.
- The car stalling or cutting out once the battery has drained, sometimes with several warning lights coming on at once.
If the battery light comes on while driving, switch off anything you don't need, such as the heated rear screen, seat heaters and air conditioning, and head to a garage or somewhere safe to stop. Avoid switching the engine off until you're there, because it may not restart.
Alternator or battery: how to tell the difference
Because both problems end with a car that won't start, it's easy to blame the wrong part. A few simple checks help narrow it down:
- If the car starts with a jump but dies again soon after, the alternator probably isn't charging.
- If the car starts with a jump and then runs normally all day, but won't start the next morning, the battery is more likely the problem, or something is draining it overnight.
- If the battery warning light comes on while driving, suspect the alternator or its belt rather than the battery.
- A voltage check tells you most. With a simple multimeter across the battery terminals, a healthy battery reads about 12.6 volts with the engine off. With the engine running, a working charging system usually shows roughly 13.8 to 14.7 volts. Much less than that while running suggests the alternator isn't doing its job. Smart charging systems vary the voltage, so a garage test is the reliable answer.
Most garages and many battery fitters will test the battery and charging system for free or for a small fee. It's worth doing before buying parts. If your car won't start at all, our guide to why a car won't start covers the other likely causes, including the starter motor.
How much does an alternator replacement cost in the UK?
The cost is made up of the alternator itself and the labour to fit it. On some cars the alternator sits at the top of the engine and comes out in under an hour; on others the garage has to remove wheel arch liners, drive shafts or engine mounts to reach it, which can mean three or four hours' work. Most garages also fit a new auxiliary belt at the same time.
| Type of car | Reconditioned unit fitted (typical) | New unit fitted (typical) |
|---|---|---|
| Small petrol hatchback | £250 – £400 | £350 – £550 |
| Family car, petrol or diesel | £300 – £500 | £400 – £700 |
| Stop-start or "smart" charging system | £400 – £650 | £500 – £900 |
| Premium, large SUV or hard-to-reach unit | £500 – £850 | £650 – £1,200+ |
These are typical ranges at UK independent garages in 2026, not quotes. Main dealers usually charge more and tend to fit new parts, prices are higher in London and the South East, and the exact engine matters more than the make. Always get a written quote for your registration. For other common repairs, see our UK repair costs hub.
Reconditioned, new or repair?
Reconditioned alternators are original units that have been stripped, cleaned and rebuilt with new wear parts such as bearings, brushes and regulators. A good-quality reconditioned unit from a reputable supplier, usually with a warranty of its own, is a sensible, cheaper choice for most cars.
New alternators cost more but are the safest bet on a car you intend to keep for a long time, or where reconditioned units are hard to find.
Repairing the existing unit is sometimes possible when only the voltage regulator, brushes or a bearing has failed. Specialist auto-electricians can do this, and it can be the cheapest option, though most garages simply swap the unit to save labour time.
Whichever route you take, check the auxiliary belt and tensioner too. A slipping belt or a weak tensioner can stop a perfectly good alternator charging, and a worn belt can damage a new one.
What causes an alternator to fail?
Alternators wear out gradually. The brushes and bearings have a finite life, and the electronics are exposed to heat and vibration every time the car is driven. Many last 100,000 miles or more, but some fail much sooner. Common causes include:
- Age and mileage, which wear out the bearings, brushes and slip rings
- Oil or coolant leaks dripping onto the alternator and contaminating it
- A worn auxiliary belt or tensioner, which makes the belt slip and the alternator work harder
- Heavy electrical loads, such as aftermarket audio systems or lots of short journeys with everything switched on
- A failing battery, which forces the alternator to work flat out trying to keep it charged
- Water ingress, from deep puddles or engine washing
Some causes, such as a leaking oil seal, need fixing at the same time, or a new alternator can suffer the same fate. Our guide to making your car last covers simple habits that reduce wear on parts like this.
Can you drive with a failing alternator?
Only for a short distance, and only to get somewhere safe or to a garage. Once the alternator stops charging, the car is running on borrowed time. As the battery drains, systems start to fail, and on modern cars that can include power steering assistance, the engine management system and eventually the engine itself. Losing power on a busy road or a motorway is dangerous.
A completely flat battery can also be damaged by being drained repeatedly, so a failing alternator left unfixed can mean buying a new battery too.
Alternator replacement cost for popular UK cars
The table above groups cars by type. These are typical fitted prices for specific popular models at a UK independent garage, including VAT, using a good-quality reconditioned unit. They are estimates rather than quotes: the exact engine, whether the car has stop-start, and how hard the alternator is to reach all change the price.
| Car | Reconditioned alternator, fitted (typical) |
|---|---|
| Ford Fiesta 1.0 EcoBoost | £280 – £450 |
| Vauxhall Corsa 1.2 or 1.4 petrol | £250 – £420 |
| Volkswagen Golf 1.6 or 2.0 TDI | £350 – £600 |
| Nissan Qashqai 1.5 dCi | £350 – £600 |
| BMW 3 Series 2.0 diesel | £450 – £800 |
| Range Rover Evoque 2.0 diesel | £500 – £900 |
A new unit typically adds £100–£300. Main dealers usually fit new parts and charge higher labour rates.
Mild hybrids and belt-starter generators
Many newer cars sold as "mild hybrid", often badged MHEV, 48V, e-TSI, EcoBoost Hybrid or similar, do not have a conventional alternator. Instead they use a belt-integrated starter generator (BSG or BISG) that charges a small 48-volt battery, restarts the engine in stop-start traffic and gives a little electric assistance. It does the alternator's job and more, and it costs more to replace: typically £800–£1,800 fitted at an independent garage, and more at a main dealer. The symptoms of a failure are similar to a failing alternator, often with a hybrid system or 48V warning message as well. Our guide to hybrid and PHEV warranties explains how hybrid parts are usually treated.
How long does an alternator last?
Most alternators last 80,000 to 150,000 miles, or roughly seven to ten years of typical driving. Cars that do lots of short journeys with heavy electrical loads (heated screens, seats and lights in winter), cars with oil leaks near the alternator and cars with stop-start tend to sit at the lower end. Replacing a weak 12V battery promptly helps, because a failing battery makes the alternator work much harder.
How long does an alternator replacement take?
On many cars the job takes one to two hours, so a garage can often do it the same day if the part is in stock. Where the alternator is buried low in the engine bay, or the garage has to remove a driveshaft, wheel arch liner or engine mount to reach it, it can take three to four hours. A specific unit for a less common engine may need to be ordered, which can add a day.
Does a car warranty cover an alternator?
Often, the alternator is one of the electrical components listed in mechanical breakdown cover, but whether it is on your plan depends on your cover schedule. Check the electrical section of yours rather than assume either way.
Sudden failure of a listed part may be eligible. An alternator that stops charging because of an internal failure is the kind of fault a mechanical breakdown warranty is designed to help with, subject to the policy terms.
Batteries and belts are usually excluded. The 12-volt battery and the auxiliary belt are commonly treated as wear or service items. Our guide to wear and tear explains why.
Authorisation comes first. Don't let a garage fit a new alternator before the claim has been authorised, or you risk paying for it yourself. Our guide to making a warranty claim walks through the steps.
On ClearPath Premium, each eligible claim is covered up to £3,000 including parts, labour and VAT, with labour up to £100 an hour and a £100 excess per authorised claim. Recovery up to £60 after a covered breakdown sits within that limit. See what's covered and how to make a claim, and always defer to your policy documents.
The bottom line
A battery light while driving, dimming lights or a battery that keeps going flat are all signs to get the charging system tested before the car leaves you stranded. Most alternator replacements cost a few hundred pounds, and a good reconditioned unit is a sensible way to keep the bill down. Check the belt at the same time, and fix any leaks that may have caused the failure. To see the cover available for your car, compare our plans or read about a used car warranty.
