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15 December 2025 (updated) Alternator replacement: how much it costs and how long it takes
Is your engine struggling to start? Have you noticed that your battery is draining unusually fast, even after replacing it? If your battery warning light comes on or your car won’t start, a faulty alternator may be the root cause.
It is the main power source for the car’s electrical components, converting mechanical energy from the engine into electricity to charge the battery and power essential systems. If it's faulty, you will experience power problems such as weak lights.
Here’s everything you need to know about replacing your alternator, including the costs, estimated time, and tips on how to do it yourself.
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LUCAS Alternator
14V, 70A, M8 B+, M5 D+, 0230, Ø 55 mm
Article number: LRB00436
£82.49price incl. 20% VAT, excl. delivery costs
-13%
Article number: A6365PR
compared to
RRP
£143.45
£124.49price incl. 20% VAT, excl. delivery costs
LUCAS Alternator
14V, 50A, M6 B+, L, 0004, Ø 56 mm
Article number: LRA00471
£67.49price incl. 20% VAT, excl. delivery costs
-44%
DENSO Alternator
14V, 120A, Ø 54 mm
Article number: DAN1119
compared to
RRP
£324.60
£178.99price incl. 20% VAT, free delivery
-9%
Article number: 695.002.035.050
compared to
RRP
£81.54
£73.99price incl. 20% VAT, excl. delivery costs
Common signs of a failing alternator
Before replacing anything, you’ll need to check the symptoms:
- Dashboard warning light (usually shaped like a battery)
- Dim or flickering headlights
- Strange noises from the engine bay (squealing or grinding)
- Weak or dead battery
- Electrical issues such as malfunctioning windows or infotainment systems
These symptoms may also point to a faulty car alternator voltage regulator, which controls the voltage sent to the battery. If this part fails, replacing the full alternator is usually the most efficient solution.
How much does an alternator replacement cost?
The cost of a new car alternator varies depending on the make and model of your vehicle:
| Vehicle Type | Approximate Price Range |
|---|---|
| Small cars (e.g. Ford Fiesta) | £85 – £200 |
| Family cars (e.g. Ford Focus ) | £150 – £300 |
| Premium models (e.g. BMW, Audi) | £250 – £600 |
Used or remanufactured alternators may be a cost-effective choice for older vehicles, especially when their market value is low. However, it’s advisable to look for parts with a warranty and good reliability ratings or reviews.
Replacing an alternator – step by step
Estimated time: 1–2.5 hours
Difficulty: intermediate – some mechanical experience and tools required
Tools you may need: spanners, socket set, torque wrench, Allen hex key, fixing pin, multimeter
NOTE: read the repair manual for your specific vehicle for in-depth instructions and diagrams. The car must be switched off at all times throughout the process.
1. Disconnect the battery
Before starting any electrical work, disconnect the battery:
- First, remove the negative terminal
- Then, remove the positive terminal
This order is essential for safety and to prevent short circuits or damage.
2. Access the alternator
Depending on your vehicle, you may need to remove:
- The trim panel or undertray
- Headlights or radiator grille
- Air filter housing or coolant hoses (temporarily)
Locate the alternator, it’s usually driven by the engine via a serpentine or V-belt.
3. Remove the belt
- Use a spanner to release tension from the belt first
- Hold the belt tensioner in place using a fixing pin or Allen key
- Carefully slide the belt off the alternator pulley
Make a mental note (or take a photo) of the belt routing if you're unfamiliar with it.
4. Disconnect electrical connections
The alternator has one or more cables connected to it:
- Carefully unplug the connectors or unscrew terminals
- Set the cables aside, being careful not to damage them
5. Unbolt the alternator
- Unscrew all mounting bolts holding the alternator in place
- You may need to remove components that get in the way, such as brackets or hoses
- Carefully extract the old part from the engine bay
6. Fit the new alternator
- Compare the old and new alternators to ensure they match (dimensions, shape, etc.)
- Position the new alternator in place
- Reinsert and tighten the bolts (follow the manufacturer’s torque settings)
The alternator should sit firmly: if it moves or rattles, recheck the mounting points.
7. Reconnect electrical plugs
Plug all wires and connectors back into the new alternator:
- Ensure firm, corrosion-free contacts
- Reinstall any components that were previously removed
8. Refit the belt
- Carefully loop the belt around the alternator pulley
- Release the tensioner to tighten the belt
- Double-check that the belt is aligned correctly on all pulleys
9. Reconnect the battery
- First, attach the positive terminal
- Then, the negative terminal
- Secure both firmly to ensure proper contact
Checking and testing the alternator
- After the replacement, start the engine and check whether the battery warning light turns off. It is also a good idea to take a test drive.
- Listen out for any unusual noises.
- Use a multimeter to verify voltage output (typically 13.5–14.8V with the engine running).
For a more detailed description of how to test an alternator, AUTODOC experts have made this video guide:
How long does it take to replace the alternator?
If you’re a confident DIY mechanic, replacing an alternator can take as little as 1–2 hours. Professional workshops typically complete the job in under an hour. For beginners, allow extra time to double-check each step and handle unfamiliar components. Some vehicle designs require you to remove more parts to gain access, requiring more time.
Pro tips for alternator replacement
- Always wear safety gloves and disconnect the battery before working.
- Inspect the belt for wear. Replace it if it’s cracked or frayed.
- Keep a photo or diagram of the belt routing for reinstallation.
- Consider replacing the tensioner if it feels weak or noisy.
Concluding note
Replacing a car alternator might seem daunting at first, but with the right tools and careful preparation, it’s manageable for experienced DIYers. Whether you're trying to save money or just enjoy doing your own maintenance, this repair can keep your vehicle running reliably for years to come.
Don’t forget to check out the blog and follow our YouTube channel to stay updated on the latest maintenance tips!
A useful video on this topic
DIY alternator repair
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