A low keyfob battery is a hassle. It takes under two minutes for an experienced person to change one, and the batteries cost under a dollar. Simple, low-cost devices like Chromebooks can sense and tell you the percentage charge left in a wireless mouse, but for some reason, with five-figure cars the keyfob always has to sneak up on us. Why in the world don't dealers just check and change them every time you are in for service?
The good news is that changing a keyfob battery is relatively simple. We will use Mazda as an example because we had one on hand, but most models follow similar steps, and your owner's manual should have images and instructions.
Step One - Find Out What Battery You Need and Order Some Online
Before you take your fob apart, look in your owner’s manual to see what type of LiCB battery your fob accepts. Our Mazda uses a CR2025. We purchased ten of them on Amazon for about $5. So, each one only costs about fifty cents. If you go to a hardware store or a store that helps with watch batteries, they will charge more but may have the battery on the shelf. Our battery arrived within 20 hours of our order. (Amazon Prime).
Step Two - Prepare Your Tool
Mazda suggests that a flathead screwdriver with tape over the tip is the tool you need. We followed the instructions, and we were glad we did.
Step Three - Open the Fob Case
The fob case opens in our Mazda by first using the little level to release the hidden mechanical key. This key can open your locked driver’s door even if the fob is not working. So it is handy to know how to open your fob to release the mechanical key.
Once the key is out, the fob has a small detent into which a screwdriver tip can be placed. One gentle (very gentle) twist helped the case to begin to come apart. We then slipped the screwdriver tip along the seam of the case, and it popped into two parts.
One part has a circular battery cover. Our manual said it would twist off, but in fact, it was different in appearance than the manual showed. We used a thumbnail to lift it up gently, and it revealed the battery.
Step Three - Replace the Battery
Any time you replace anything in a car, take some pictures. That way, if you get goofed up, you can look back and see how things were arranged as you disassembled them. The Battery is a small coin-like disk. It is different on the top and bottom. We will call the top the section with the printing on it. That is “Up” in our assembly, so we removed the old battery and replaced it with the new one. We then set aside the old battery for proper recycling.
Step Four - Re-assemble the Fob
Putting the fob back together is as simple as mating the two halves and snapping them together. A gentle squeeze cliche the two halves together securely. We then tested the battery, and it worked fine.
We kept our keyfob batteries in a small bag, which we labeled “CX-5.” These small button batteries have a very long shelf life, so one package may well be enough for the vehicle's life.
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Images by John Goreham
John Goreham is a long-time New England Motor Press Association member and recovering engineer. John's interest in EVs goes back to 1990 when he designed the thermal control system for an EV battery as part of an academic team. After earning his mechanical engineering degree, John completed a marketing program at Northeastern University and worked with automotive component manufacturers, in the semiconductor industry, and in biotech. In addition to Torque News, John's work has appeared in print in dozens of American news outlets and he provides reviews to many vehicle shopping sites. You can follow John on TikTok @ToknCars, on Twitter, and view his credentials at Linkedin
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