What Size Battery for a Key Fob? A Comprehensive Guide

Is your car key fob acting up? Do you find yourself pressing the unlock button multiple times before your car finally responds? It’s a common frustration, and more often than not, the culprit is a dead or dying key fob battery. Before you rush to a dealership or repair shop, you should know that replacing your key fob battery is often a simple DIY task. But first things first, you need to know what size battery for your key fob is required.

Knowing the correct battery size is crucial for a successful key fob battery replacement. Using the wrong size can prevent your key fob from working, or even damage it. This guide will walk you through everything you need to know about finding the right battery size for your key fob and replacing it yourself, saving you time and money.

Identifying the Correct Key Fob Battery Size

Before you even think about opening your key fob, let’s explore the ways you can determine the correct battery size it needs. There are several methods, ranging from a quick visual check to a little bit of detective work.

1. Check Your Key Fob Itself

The easiest way to find out what size battery your key fob requires is to look directly at the key fob itself. Many manufacturers will emboss or print the battery size information directly onto the key fob casing.

Look on the Back: Examine the back of your key fob casing closely. Sometimes, you’ll find small markings indicating the battery type. This is often a series of letters and numbers, such as “CR2032” or “CR1620”.
Inside the Key Sleeve: If your key fob has a physical key that slides out, remove the key and check inside the cavity. Some manufacturers place the battery information in this hidden location.

Opening a key fob with a watch knife to reveal the battery compartment.

2. Gently Open Your Key Fob (If You Can)

If you can’t find the battery size on the exterior of your key fob, the next step is to carefully open it. You might be able to do this without tools, or you may need a small, flat tool.

Look for a Notch: Many key fobs have a small notch or slot somewhere along the seam of the casing. This notch is designed to help you pry the case open.
Use a Thin Blade: If you find a notch, or if the case seems to have a visible seam, you can use a thin, flat blade like a watch knife or a small flathead screwdriver. Gently insert the blade into the notch or seam and carefully twist or pry to begin separating the two halves of the key fob case. Important: Be gentle and avoid forcing it, as you don’t want to damage the casing.
Once Open, Note the Battery: Once you have the key fob open, you will see the battery. The battery size should be printed directly on the battery itself. Make a note of this size. Common sizes include CR2032, CR2025, CR2016, and others.

3. Consult Your Vehicle’s Owner’s Manual

Your vehicle’s owner’s manual is a treasure trove of information, and it often includes details about your key fob, including the battery type it uses.

Locate the Key Fob Section: Look in the index or table of contents for sections related to “keys,” “remote control,” “keyless entry,” or “key fob.”
Battery Specifications: Within this section, you should find information about the key fob battery, including the size and type. The manual might specify something like “CR2032 battery” or provide a part number.

4. Online Resources and Battery Finder Tools

If you’re still unsure about the battery size, the internet can be a valuable resource.

Manufacturer Websites: Visit the website of your car’s manufacturer. Many manufacturers have online owner’s manuals or FAQ sections where you can search for key fob battery information by vehicle make, model, and year.
Online Battery Finders: Some battery retailers and websites specialize in batteries and offer online tools to help you find the right battery for your key fob. You typically enter your vehicle’s make, model, and year, and the tool will suggest the compatible key fob battery size.

Common Key Fob Battery Sizes

While there can be variations depending on the car make, model, and year, some battery sizes are much more common in key fobs than others. Knowing these common sizes can help you narrow down your search.

CR2032 Battery: This is by far the most common key fob battery size. It’s a 3V lithium coin cell battery that is widely available and relatively inexpensive. Many car manufacturers, from Honda to BMW, use CR2032 batteries in their key fobs.
CR2025 Battery: Another 3V lithium coin cell battery, the CR2025 is slightly thinner than the CR2032. It is sometimes used in key fobs where space is a tighter constraint. While a CR2032 is often interchangeable with a CR2025 in a pinch, it’s always best to use the exact recommended size if possible.
CR2016 Battery: This is a thinner 3V lithium coin cell battery than both the CR2032 and CR2025. It’s less common in key fobs than the CR2032 but is still used in some models.
Other Less Common Sizes: You might occasionally encounter other battery sizes like CR1632, CR1620, CR1220, or CR1225. These are less frequent but important to be aware of. Some older key fobs or those from specific manufacturers might utilize these less common sizes. For example, the original article mentioned the Honda CR-V using a CR1250 battery (note: this might be a typo and could refer to CR1220 or CR1225, further checking is advisable based on the specific CR-V year). Ford Mustang key fobs are also mentioned as sometimes requiring two batteries.

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

Once you’ve determined the correct battery size for your key fob, you’re ready to replace it. Here’s a step-by-step guide based on best practices and the original article:

Tools You’ll Need:

New Battery: The correct size battery for your key fob (e.g., CR2032).
Thin Blade or Pry Tool: A watch knife, small flathead screwdriver, or a specialized plastic pry tool designed for electronics.
Precision Screwdriver (Possibly): Some key fobs use tiny screws to secure the case. If you see screws, you’ll need a precision screwdriver set with the appropriate size (usually 1.4mm to 2.4mm).
Tweezers (Optional but Recommended): Tweezers can be helpful for handling the small battery and positioning it correctly.
Your Smartphone Camera: This is crucial for taking a reference photo!

Steps:

Prepare Your Workspace: Work on a clean, well-lit surface. Having a soft cloth underneath can prevent scratches and stop small parts from rolling away.
Open the Key Fob Casing: Using your chosen tool (thin blade or pry tool), gently pry open the key fob case at the notch or seam you identified earlier. Work your tool around the perimeter of the case, gently separating the two halves. Avoid forcing it. If there are screws, remove them first with your precision screwdriver.
Take a Photo! Before you remove the old battery, use your smartphone to take a clear photo of the inside of the key fob. This photo is invaluable as a reference for how everything goes back together, especially the battery orientation (+ and – sides).
Remove the Old Battery: Carefully remove the old battery. In some key fobs, the battery might be held in place by a small clip or metal contact. Use tweezers or your fingertip to gently lift the battery out. Note the orientation of the battery (positive (+) and negative (-) sides).
Install the New Battery: Install the new battery in the same orientation as the old one. The positive (+) side of the battery usually faces up, but always double-check your reference photo. Ensure the battery is securely seated in its compartment.
Close the Key Fob Casing: Carefully snap the two halves of the key fob case back together. Make sure they are firmly closed and that there are no gaps. If you removed screws, replace and tighten them gently.
Test Your Key Fob: Test your key fob to ensure it’s working correctly. Try unlocking and locking your car remotely.

Installing a new CR2032 battery into a car key fob remote.

Important Tips and Precautions

Gentle is Key: Always be gentle when opening and handling your key fob. Forcing anything can damage the delicate internal components.
Reference Photo is Your Friend: Taking a photo before removing the battery is the single most important step to ensure a smooth reassembly.
Battery Orientation Matters: Pay close attention to the positive (+) and negative (-) orientation of the old battery and install the new one in the same way.
Avoid Touching Circuit Board Components: Try to handle only the battery and the casing. Avoid touching or disturbing any other components inside the key fob, especially the circuit board and wiring, unless necessary for battery removal and replacement.
Proper Battery Disposal: Dispose of the old lithium battery responsibly according to local regulations. Many battery retailers offer battery recycling programs.
If in Doubt, Seek Professional Help: If you are uncomfortable performing this DIY task or if you encounter any difficulties, don’t hesitate to seek help from a professional. Car dealerships, auto repair shops, and specialized battery centers can replace your key fob battery for you.

Replacing your key fob battery is a straightforward task once you know what size battery for your key fob you need. By following these steps and taking your time, you can restore your key fob to working order and avoid unnecessary expenses.