Car Key Fob Battery Replacement: DIY Guide & When to Call a Pro

Is your car key fob not working like it used to? Before you head to the dealership, the fix might be as simple as replacing the battery. In this guide, we cover the most common key fob batteries, walk you through a DIY replacement, and explain when you should call a professional locksmith instead.

Common Key Fob Battery Types

Most car key fobs use small, flat coin-cell batteries that you can find at any pharmacy, hardware store, or online. The three most common types are:

• CR2032 — The most widely used key fob battery. Found in many Toyota, Honda, Ford, Chevrolet, and Hyundai fobs.
• CR2025 — Slightly thinner than the CR2032. Common in some Nissan, Mazda, and Chrysler fobs.
• CR2016 — The thinnest of the three. Used in select Honda, Toyota, and Lexus fobs.

You can usually find the correct battery type printed on the old battery itself, in your vehicle owner’s manual, or by searching your car’s make, model, and year online.

Step-by-Step: How to Replace Your Key Fob Battery

For most key fobs, replacing the battery is a straightforward process that takes less than five minutes. Here is how to do it:

Step 1: Find the Seam or Release Button

Look at your key fob closely. Most fobs have a small notch, seam, or sliding release button on the side or back. Some fobs have a small physical key built in — slide it out first, as it often reveals the battery compartment release.

Step 2: Open the Fob

Use a small flathead screwdriver, a coin, or your fingernail to gently pry the fob open along the seam. Work slowly and carefully to avoid cracking the plastic housing. If your fob has screws, use a small Phillips-head screwdriver to remove them first.

Step 3: Note the Battery Orientation

Before removing the old battery, pay attention to which side is facing up — the positive (+) side or the negative (-) side. This is important because installing the new battery the wrong way around will prevent the fob from working.

Step 4: Replace the Battery

Remove the old battery and insert the new one in the same orientation. Press it firmly into place. Make sure it sits flat and secure in the battery holder.

Step 5: Reassemble and Test

Snap the fob back together (you should hear a click) and test all the buttons — lock, unlock, trunk release, and panic. If everything works, you are done.

Which Cars Are Harder to DIY?

While most key fobs are easy to open, some are more challenging:

• Some Lexus models — Certain Lexus smart keys have sealed housings that are difficult to open without the right tools.
• BMW comfort access keys — These rechargeable fobs do not use a standard replaceable battery. They charge in the ignition slot and may need professional service when the internal battery degrades.
• Some Mercedes-Benz keys — Chrome-cased keys can be tricky to open without scratching or damaging the housing.
• Sealed smart keys — A few newer vehicles use fobs that are not designed for user battery replacement at all.

If your fob is difficult to open or you are worried about breaking it, a locksmith can handle the battery swap quickly and safely.

Key Fob Not Working After Battery Replacement?

If you replaced the battery and your fob still does not work, the issue may not be the battery. Here are some common reasons:

• Battery installed incorrectly — Double-check the orientation. The + and – sides must match the original placement.
• Fob needs reprogramming — Some vehicles lose their fob pairing when the battery is removed, especially if the fob was dead for a long time. Reprogramming may require a professional locksmith or dealer.
• Damaged internal contacts — If the battery contacts inside the fob are corroded or bent, the fob will not work even with a fresh battery.
• Fob circuit board failure — Like any electronic device, key fob circuit boards can fail over time.
• Dead backup battery in the car — If your car’s own battery is dead, the fob may not communicate with the vehicle.

If a new battery does not fix the problem, it is time to call a locksmith. King Locksmith Atlanta can diagnose and fix key fob issues on site, including reprogramming. Check out our car key replacement and car locksmith services for more information.

When to Call a Professional

Call a locksmith for key fob help when:

• You cannot open the fob without risking damage.
• The fob does not work after a battery change and needs reprogramming.
• You need a completely new key fob — not just a battery.
• Your vehicle uses a non-standard rechargeable fob.

King Locksmith Atlanta provides mobile key fob service throughout Metro Atlanta. We come to your location, diagnose the issue, and fix it on the spot. Call (404) 383-4426 for fast key fob assistance.