What Size Battery Goes in a Key Fob? A Comprehensive Guide

It’s a familiar scenario for many car owners: you press the unlock button on your key fob, but your car takes its time to respond, or perhaps doesn’t respond at all on the first try. This frustrating delay can often point to a simple culprit – a weakening battery in your key fob. Before you assume you need a costly key fob replacement, consider the most straightforward solution: replacing the battery yourself.

Modern car key fobs, remotes, and transponders rely on small batteries to operate, and like any battery, these will eventually wear out. While taking your vehicle to a dealership or a mechanic for a key fob battery replacement is an option, it’s often unnecessary and can be more expensive than you might expect. The good news is that replacing a key fob battery is a DIY task that most car owners can handle with a few basic tools and a little patience.

But before you start prying open your key fob, the most important question is: What Size Battery Goes In A Key Fob? Using the correct battery size is crucial for ensuring your key fob functions correctly and avoids any potential damage. This guide will walk you through how to determine the right battery size for your key fob and how to replace it yourself, saving you time and money.

Identifying the Right Key Fob Battery Size

Finding the correct replacement battery size is the first and most critical step. Luckily, there are a couple of ways to determine what size battery your key fob requires.

Check Your Key Fob for Markings

The easiest way to find out what size battery you need is to check your key fob itself. Many key fobs have markings indicating the battery type directly on the case.

Look on the back of the fob: Carefully examine the back of your key fob. Sometimes, manufacturers will emboss or print the battery size directly onto the plastic casing.
Check inside the key sleeve: If your key fob has a separate key that slides out, remove the key and inspect the area underneath. There might be battery size information located here.

These markings are usually a combination of letters and numbers, such as CR2032, CR1620, or CR2450. These codes refer to standard coin cell battery sizes, and understanding these designations is key to getting the right replacement.

Opening Your Key Fob to Identify the Battery

If you can’t find any markings on the exterior of your key fob, don’t worry. You’ll need to carefully open the fob to visually identify the battery size. This process sounds daunting, but with the right tools and a gentle approach, it’s quite manageable.

To open your key fob, you’ll typically need:

A thin, flat tool: A watch knife or a small, flat-head screwdriver works well for gently prying open the plastic case.
Precision screwdriver (possibly): Some key fobs use tiny screws to hold the case together. You might need a precision screwdriver set (ranging from 1.4mm to 2.4mm) if you see screws.

Steps to open your key fob:

Inspect for screws: Carefully look around the edges of your key fob for any small screws. If you find them, use the appropriate precision screwdriver to remove them and set them aside in a safe place.
Locate the seam: Find the seam where the two halves of the key fob case join together.
Gently pry it open: Insert your thin, flat tool into the seam. Apply gentle pressure and twist or lever the tool to start separating the case halves. Work your tool around the seam gradually, like peeling an orange, until the case pops open. Avoid forcing it open at just one point, as this can damage the case.

Once your key fob is open:

Identify the battery: You’ll see the battery inside. Note the code printed on the battery itself. This code (like CR2032) is the battery size you need.
Take a picture: Before removing the old battery, take a photo with your phone. This is a crucial step! Key fobs can have different internal layouts, and a photo will help you remember the battery orientation (positive side up or down) and the placement of any small parts.

Common Key Fob Battery Sizes

While battery sizes can vary depending on your car’s year, make, and model, some battery sizes are more common than others in key fobs.

CR2032: This is perhaps the most common key fob battery size. It’s a 20mm diameter, 3.2mm thick coin cell battery.
CR2025: Similar to CR2032 but slightly thinner (2.5mm thick). Sometimes interchangeable with CR2032, but check your fob’s requirements if space is tight.
CR2016: Thinner still (1.6mm thick), another variation in the CR20xx family.
CR1620: Smaller diameter (16mm) and 2.0mm thick.
CR2450: Larger diameter (24.5mm) and thicker (5.0mm), used in some key fobs requiring more power or longer life.
CR1220 & CR1250: Smaller batteries, sometimes found in simpler key fobs or older models. For example, the Honda CR-V has been known to use a CR1250 battery.

Important Note: Some key fobs, like those in Ford Mustangs, may even use two batteries. Always confirm the number and size of batteries your specific key fob requires.

Step-by-Step Guide to Replacing Your Key Fob Battery

Once you’ve identified the correct battery size, replacing it is a straightforward process.

Tools you’ll need:

New key fob battery: Make sure you have the correct size!
Thin, flat tool: Watch knife or small screwdriver (used for opening).
Precision screwdriver (if needed): For screws.
Tweezers (optional): Helpful for handling the small battery.

Steps to replace the battery:

Open the key fob: Follow the steps outlined earlier to open your key fob case.
Remove the old battery: Use tweezers or your fingers to gently lift the old battery out of its compartment. Pay attention to the battery’s orientation – note which side is facing up (usually the positive side with a “+” marking).
Insert the new battery: Place the new battery into the compartment, ensuring the correct orientation (positive side up if that’s how the old one was). It should snap or slide into place.
Close the key fob: Carefully align the two halves of the key fob case and snap them back together. If there were screws, replace and tighten them gently.
Test your key fob: Try using your key fob to lock and unlock your car to ensure the new battery is working.

Important Tips and Precautions:

Work in a clean, well-lit area: This will help you keep track of small parts.
Be gentle: Don’t force anything when opening or closing the key fob.
Don’t touch the circuit board: Avoid touching the circuit board or any wiring inside the key fob, as static electricity or damage could cause problems.
Dispose of old batteries properly: Lithium coin cell batteries should be recycled according to local regulations.

Where to Get Key Fob Batteries and Replacements

You can find replacement key fob batteries at various locations:

Retail stores: Most drugstores, supermarkets, and electronics stores carry common coin cell batteries like CR2032.
Auto parts stores: Auto parts stores will also stock key fob batteries and can often help you identify the correct size.
Interstate All Battery Center: For a wide selection of batteries, including key fob batteries, and expert advice, visit your local Interstate All Battery Center. They also offer key fob replacement services if you prefer professional help.

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Conclusion

Knowing “what size battery goes in a key fob” is the first step towards a quick and easy DIY fix for a common car problem. By taking the time to identify the correct battery and following these simple steps, you can replace your key fob battery yourself, saving money and avoiding unnecessary trips to the dealership. For reliable replacement batteries and expert assistance, remember to check out Interstate All Battery Center for all your battery needs.