Replace a Car Key Fob Battery: interactive 3D repair guide

All 5 steps

1. 1Slide the catch, pull out the emergency key

   Slide the small catch on the key’s edge towards its middle and pull the emergency key out by its head: the metal blade slides out of its channel. Lay it on the mat. At the mouth of its empty channel is the slot that opens the shell.

2. 2Twist the halves apart at the slot trap

   At the mouth of the empty key channel, where the key came out, a narrow slot opens in the seam. Put the screwdriver’s taped tip into it and turn it a little, a quarter turn at most: the halves spring apart at that end. Then run the plastic pry tool round the seam, so the clips on the sides let go one by one. Never lever at the buttons’ side. Avoid this trap: With no slot on that side, the knife has to be forced into the seam under the buttons. It slips through the thin edge of the rubber keypad and into the board beside it, scoring one of the fine copper tracks that join the buttons to the chip: that button is now dead, and the knife’s edge has marked the shell too. Open the key only at its slot, with a taped flat tool.

3. 3Lift the back off, transponder still in place trap

   Lift the back half straight up off the board and turn it inside up at once, low over the mat, before you set it down. In its corner, in a little pocket of its own, sits the transponder chip that the car’s immobiliser reads before the engine will start; it is loose there, so it stays in its pocket only while that side is up. Avoid this trap: Lifted off inside down and tipped to look, the back half lets the transponder chip slide out of its pocket: it drops onto the mat and bounces away. The buttons may still lock the doors, but without the chip the immobiliser will not let the engine start, and a lost one has to be replaced and paired by a dealer or a locksmith. Turn the back inside up as you lift it, and check the chip is there before you go on.

4. 4Note the + side, lift the old cell out

   Look at the old cell before it moves: here its + side, the flat side with the writing, faces up, away from the board, as it does in many keys; in some it faces the board. Note which way, or take a photo. Then slip the plastic pry tool into the notch beside the holder, lift the cell’s edge and slide it out from under its clip, and put it in the tray.

5. 5Fit the new cell the same way up trap

   Check the new cell’s size against the old one’s print: CR2032 here. Holding it by its edges, + side up as the old one was, slide it under the holder’s clip and press it flat until it seats. Avoid this trap: Pressed in upside down, the new cell sits just as snugly under its clip, but now its + side is on the board’s − pad and the clip touches its − side. The key does nothing: no light, no unlocking, as if the cell were still flat. Take it out and turn it over: + side the way the old one was.

What you need

• A new coin cell · the size on the old one (CR2032 here), from a known brand
• A small flathead screwdriver · its tip wrapped in tape, or a coin for some keys
• A plastic pry tool · never a knife or anything metal on the board
• Insulating tape · for the old cell’s faces

Questions

Safety

Keep coin cells, new and old, away from children: open the new one’s child-resistant pack only when the key is open, and tape the old one’s faces before it goes to recycling. Buy a known brand’s cell, the size printed on the old one. Use plastic, not metal, near the board, hold the cell by its edges, and never force a blade into the key’s seam.

• Coin cells: keep button and coin batteries, new and old, away from children: one that is swallowed can burn through tissue within hours. If you think one has been swallowed, get emergency help at once. Tape an old cell’s faces before you recycle it.
• Static (ESD): work on an anti-static mat with a grounded wrist strap; a spark you cannot feel can kill a chip.

About this guide

3D Spatial Reconstruction: models are engineered from factual measurements to show the parts, the fixings and the order of the job before you start. Always check the handbook of your own car.

The key is a generic remote key of our own design, not one maker’s: the common kinds’ parts in our own shell. Like most smart keys it has an emergency key blade released by a catch, and a slot by the blade’s channel where a flat tool opens it; like many older remote keys it has its immobiliser transponder as a chip of its own, loose in a pocket of the shell, where in most newer keys it is part of the board. The order is the one makers’ handbooks give: the mechanical key out first, a flat tool wrapped in tape or a cloth in the slot (Nissan and Honda say so), the new cell the right way up, the halves pressed together and the buttons tried.

Which way up the cell goes depends on the key: in ours, as in many, its + side faces up, away from the board; Nissan’s LEAF handbook puts it towards the bottom of the case, and Honda’s SMART Key handbook for the FORZA 750 says negative side up. Note the old one’s way before it comes out. The brief’s knife trap is our picture of what forcing a blade into the buttons’ side does; the handbooks themselves say only not to touch the board or force the case.

A CR2032 and a CR2025 are both 20 mm across; the CR2032 is 3.2 mm thick and about 235 mAh, the CR2025 2.5 mm and about 170 mAh (Energizer’s datasheets), so fit the size printed on the old one. The transponder’s size is our estimate. The $4 is a two-pack of a known brand’s CR2032 at a US shop; what a shop charges to fit one varies too much to give a figure. The 3D runs faster than real hands do.

Sources: Nissan: LEAF 2023 owner’s manual, Intelligent Key battery (the mechanical key out, a small flat-blade screwdriver in the corner slit and twisted, a cloth to protect the case, CR2025, the + side to the bottom of the case, hold it by its edges, do not touch the circuit), Nissan: LEAF 2025 owner’s manual, Intelligent Key battery (CR2032, the slits on both sides, the + side to the bottom, the coin cell danger to children), Honda: FORZA 750 owner’s manual, SMART Key battery (CR2032, a coin or a flat-head screwdriver wrapped in cloth in the slit, negative side up, do not touch the circuit, do not force the key apart), Kia: owner’s manual, smart key battery (the mechanical key off first, CR2032, the battery’s position, a swallowed cell can injure fatally within 2 hours), Energizer: CR2032 datasheet (3 V, 235 mAh, 20.0 × 3.2 mm, the warning to keep it from children), Energizer: CR2025 datasheet (3 V, 170 mAh, 20.0 × 2.5 mm), CPSC: Reese’s Law (child-resistant packaging for button and coin cells, sold from 2023; a swallowed cell can burn through a child’s throat in two hours), Locksmith Ledger: harvesting transponder chips (glass or ceramic chips in a key’s head; in keys with a board it is built into the board, except Honda’s), Car Key Action: what a transponder key is (a separate part in older remotes; without the right chip the engine will not start), Price: Target, Energizer 2032 lithium coin batteries, 2-pack, $3.99 (October 2026).

The 3D models, drawings and text are our own. The car shown is a generic one of our own design, not any one maker’s model.