When your car fob has stopped responding, only works at short range, or requires multiple button presses, the most common cause is a flat battery. Luckily, changing a battery is usually a 5 minute job that you can do at home.
Typically, a car battery replacement will restore your fob to working order, if this isn’t the case, our professional auto locksmiths can diagnose the issue and get you back on the road quickly.
This is the definitive guide to how to change your car battery. Our auto locksmith experts have combined all their knowledge and expertise to highlight common mistakes drivers make when changing their car battery. We also cover the popular types of car battery in the UK, when DIY is appropriate versus when to call a locksmith, and a handy battery reference table organized by car make.
Signs Your Car Key Battery Needs Replacing
Before you do anything it’s helpful to recognise the most common signs that your car fob battery is weak.
Symptoms include:
- Reduced locking / unlocking range – You need to stand closer than usual
- Intermittent response – The key fob works inconsistently
- Multiple button presses required – Before the car responds
- Dim or no LED light – On the fob when the lock button is pressed
- Dashboard warning messages – Such as “Key not detected” or “Key battery low”
These issues almost always indicate that the key fob battery is running out of power. Replacing the car key battery is the simplest and cheapest fix.
What Battery Does My Car Key Use?
Most modern car key fobs use lithium coin batteries with a CR prefix:
- CR2032
- CR2025
- CR2016
- CR2450
These codes refer to the battery’s size and thickness. The exact type depends on the car manufacturer and the key design.
The easiest way to confirm the correct car key battery is to open the fob and check the code printed on the old battery.
Check this reference table for common UK makes.
| Car Make | Common Battery | Notes |
|---|---|---|
| Ford | CR2032 | Most Focus, Fiesta, Transit models |
| Volkswagen | CR2032 | Golf, Polo, Passat flip keys |
| BMW | CR2032 / CR2450 | Comfort Access fobs use CR2450 |
| Mercedes | CR2025 | Most modern key fobs |
| Toyota | CR2032 / CR1632 | Varies by model year |
| Vauxhall | CR2032 | Corsa, Astra, Insignia |
| Nissan | CR2032 | Qashqai, Juke Intelligent Key |
Locksmith’s tip: Replacing a key fob battery requires very little equipment. You’ll need a small flathead screwdriver or coin, a compatible replacement battery, and clean cloth or gloves to avoid leaving fingerprints on the battery.
How to Change Your Car Key Battery – Step by Step
Follow these simple rules to replace your battery safely.
- Remove the mechanical key blade – Many modern keys have a hidden manual emergency key. Press the release button and slide the blade out
- Locate the seam or notch on the fob – Look around the edge of the fob for a small gap or indentation where the casing separates
- Gently pry open the casing – Insert a small coin or screwdriver into the seam and twist gently until the casing pops open
- Check the battery orientation – Before removing the old battery, note which side faces up, and place the new battery the same way
- Remove the old battery – Carefully lift it out with your fingernail or use the screwdriver
- Insert the new battery – Place the new battery in the correct way up (often + side up)
- Close the fob – Align the casing and press firmly until it clicks back into place
- Test the key fob – Stand near your vehicle and test the lock and unlock buttons to ensure everything works correctly
Car Key Still Not Working After Battery Replacement?
If your fob is still not working after a battery replacement, there may be another problem with it.
Common failures are caused by:
Wrong battery type – Using the wrong battery size can prevent proper contact.
Incorrect polarity – If the battery is upside down, the key won’t receive power.
Fob needs resyncing – Some vehicles require the key to be reprogrammed after a battery change.
Damaged contacts inside the fob – Wear or corrosion can stop the battery connecting properly.
Water or physical damage – Dropping the key or exposing it to moisture can damage internal electronics.
If your issue isn’t solved by troubleshooting, our professional locksmiths can diagnose the fault quickly. In many cases, we can repair the key without needing to replace it.
When to Call a Professional Auto Locksmith
While replacing a battery is usually straightforward, there are situations when professional help is the best option.
Consider contacting one of our professional locksmiths when the key fob is damaged or won’t close properly, the battery drains repeatedly in weeks, the key needs programming or re-syncing, the buttons or internal circuit board are damaged, or you’ve lost your car keys completely.
In these cases our expert auto locksmiths can often repair your key fob on the spot, wherever you are.
Our urgent auto locksmith services provide:
- Mobile key diagnostics
- Auto key repair
- Replacement key programming
- Emergency key access
If your key cannot be repaired, you may need a full car key replacement service. Our mobile locksmiths cover Essex and surrounding areas and can usually resolve your issue the same day.
Frequently Asked Questions
Can I use any battery in my car key?
No, car key fobs require specific lithium coin batteries, CR2032 or CR2025. Using the wrong size battery may prevent proper contact or damage the key.
How long do car key fob batteries last?
Most car key batteries last 2-4 years, depending on how often they are used and the vehicle’s system. You can learn more in our blog: How Long Do Car Key Batteries Last.
Do Halfords replace car key batteries?
Yes, many Halfords stores offer battery replacement services for key fobs. However, it is often quicker and cheaper to replace your battery yourself using the steps above.
Does my car need reprogramming after a battery change?
Usually not, most vehicles are not affected by a battery replacement. If the key stops working afterwards, a locksmith can diagnose whether the key requires repair or replacement.
How much does it cost to replace a car key battery?
Coin batteries usually cost between £2-£5 depending on the brand and size. If the issue is more complex, one of our locksmiths can diagnose whether the key requires repair or replacement.
Final locksmith tip
When opening your key fob, always work wgently. One of the most common mistakes we see drivers make is forcing the key casing open and snapping the plastic clips. If that happens, the key may require professional auto key repair instead of a simple battery change.
If you would rather avoid the risk, Urgent Auto Locksmith can replace your key battery, repair damaged fobs, or supply a fully programmed replacement key.
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