Maintenance procedure · Written to ASD-STE100 Issue 9 · Formatted to ANSI Z535

Replace the Battery in a Vehicle Key Fob

Coin cell replacement in a remote or smart key — the cell type is per vehicle, so this page shows you where to read it instead of guessing it for you
ApplicabilityRemote keyless entry fobs and smart keys in passenger cars and light trucks that use a user-replaceable lithium coin cell
Task time18 min to 52 min editorial estimate, not a measurement
PersonnelOne
Revisionv4 · 2026-08-04
BEFORE YOU BEGIN

Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.

Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.

Summary

A key fob that only works when you are standing next to the car is usually a flat coin cell rather than a broken remote. Mazda's owner's manual lists a reduced operational range as one of the three signs that the key battery is low, alongside a flashing KEY indicator and a transmitter light that no longer blinks. Changing the cell is a five-minute job on a kitchen table. The two things that go wrong are buying the wrong cell and putting it in upside down, and both are avoidable if you read the old cell before you throw it away.

This page will not tell you which cell your fob takes, and that is deliberate. Mazda's 2018 CX-5 manual says CR2025 and Mazda's 2025 CX-30 manual says CR2032 — one manufacturer, two answers, because it depends on the fob. Kia's smart key page says CR2032, and Kia's Seltos manual describes the cell as a 3 volt lithium battery. So the page hands you the two places the right answer actually lives: the marking stamped on the cell you are taking out, and the key section of your own vehicle's documentation. It also takes the swallowing hazard seriously, because a lithium coin cell is the one part of this job that can kill a small child, and both Kia's manual and the US Consumer Product Safety Commission say so in those terms.

Safety

WARNING

KEEP EVERY BUTTON CELL AND COIN CELL AWAY FROM CHILDREN.
A swallowed button cell can burn through a child's throat in two hours. A swallowed lithium coin cell can cause severe or fatal injury in two hours. If a person swallows a cell, go to an emergency department immediately. Call the National Battery Ingestion Hotline on 800-498-8666. You can also call the Poison Help Line on 800-222-1222.

Necessary equipment

ItemNote
Thin flat toolA small flat screwdriver or a plastic opening tool is satisfactory.
Adhesive tapePut tape on the tip of the tool before you open the case.
Non-conductive tapeUse this tape on the used coin cell before disposal.
Small screwdriver optionalSome key fobs have a screw in the case.
Soft cloth optionalThe cloth keeps the small parts in one place.
Container with a lidKeep the used coin cell in the container until disposal.
New lithium coin cell materialThe type must be the same as the type of the used coin cell.

Specifications

Period in which a swallowed button cell can burn through a child's throat or esophagus
Manufacturer or standard verified
2 hours

Source: Button Cell and Coin Batteries — Safety Education Center · tier 1 · accessed 2026-07-29

Period in which a swallowed lithium button cell can cause severe or fatal injury
Manufacturer or standard verified
2 hours

Source: this product contains a button battery — Kia Owner's Manual, Battery replacement · tier 1 · accessed 2026-07-29

Prepare the work area

Estimated 4 min to 16 min

NOTEThe documentation for your vehicle gives the coin cell type and the method to open the case.
  1. Do this work on a table with good light.
    <1m
  2. Keep all children away from the work area.
    • A coin cell is a serious hazard to a child.
    <1m
  3. Find the key section in the documentation for your vehicle.
    • The documentation gives the coin cell type for your key fob.
    • The documentation gives the method to open your key fob.
    2m
  4. If you do not have the documentation, get the documentation from the vehicle manufacturer.
    • The website of the vehicle manufacturer frequently has the documentation.
    1m
  5. Put a soft cloth on the table.
    • The cloth keeps the small parts in one place.
    <1m
  6. Put tape on the tip of the tool.
    • The tape gives protection to the case of the key fob.
    <1m

Open the case of the key fob

Estimated 2 min to 6 min

Method to open the case of your key fob
Unverified — do not rely on this value
CONSULT THE DOCUMENTATION FOR YOUR VEHICLE.

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

  1. If your key fob has a mechanical key, remove the mechanical key.
    • A button or a lever releases the mechanical key.
    • The slot for the mechanical key is frequently the entry point for the tool.
    <1m
NOTICE

DO NOT USE FORCE ON THE CASE.
The case of a key fob is thin. Force can break the case.

  1. Open the case with the method in the documentation for your vehicle.
    • Some key fobs have a slot for a thin tool.
    • Some key fobs have a screw in the case.
    • Mazda and Kia both use a thin tool in a slot on the key fobs in their manuals.
    2m
  2. Put the two halves of the case on the cloth.
    <1m

Change the coin cell

Estimated 4 min to 8 min

NOTERead the type code on the used coin cell before you remove the used coin cell.
Coin cell type for your key fob
Unverified — do not rely on this value
READ THE TYPE MARKING ON THE USED COIN CELL AND CONSULT THE DOCUMENTATION FOR YOUR VEHICLE.

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

Coin cell voltage for your key fob
Unverified — do not rely on this value
CONSULT THE DOCUMENTATION FOR YOUR VEHICLE. THE COIN CELL ITSELF CARRIES THE MARKING.

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

Coin cell type that Mazda gives for the key of the 2018 CX-5
Manufacturer or standard verified
CR2025 or equivalent

Source: Key Battery Replacement — 2018 Mazda CX-5 Owner's Manual, Owner Maintenance · tier 1 · accessed 2026-07-29

Coin cell type that Mazda gives for the key of the 2025 CX-30
Manufacturer or standard verified
CR2032 or equivalent

Source: Warnings and Cautions about Key Battery Replacement — 2025 Mazda CX-30 Owner's Manual, Key Inspection · tier 1 · accessed 2026-07-29

Coin cell type that Kia gives for the smart key in the manual read for this page
Manufacturer or standard verified
CR2032

Source: Battery replacement — Smart key — Kia Owner's Manual · tier 1 · accessed 2026-07-29

Coin cell voltage that Kia gives for the folding key and the smart key
Manufacturer or standard verified
3 V

Source: Battery replacement — Kia Seltos Owner's Manual, Keys · tier 1 · accessed 2026-07-29

  1. Look at the position of the used coin cell.
    • Note which face of the coin cell is visible.
    • A photograph of the open key fob is a good record.
    <1m
  2. Read the type code on the visible face of the used coin cell.
    • The type code has letters and digits.
    • If the code is not clear, use a magnifier.
    <1m
  3. Compare the type code with the type in the documentation for your vehicle.
    <1m
  4. If the two types are different, speak to the dealer for your vehicle.
    • A different type can be an incorrect coin cell from an earlier replacement.
    <1m
WARNING

PUT THE USED COIN CELL AWAY FROM CHILDREN IMMEDIATELY AFTER REMOVAL.
A used coin cell can burn the throat of a child.

NOTICE

DO NOT TOUCH THE CIRCUIT BOARD IN THE KEY FOB.
Mazda tells you that contact with the circuit board can cause damage to the key fob.

  1. Remove the used coin cell from the holder with the covered tool.
    <1m
  2. Put the used coin cell in the container.
    • Close the lid of the container.
    <1m
  3. Hold the new coin cell by the edge.
    • Do not touch the two flat faces of the new coin cell.
    <1m
WARNING

INSTALL ONLY A COIN CELL OF THE TYPE IN THE DOCUMENTATION FOR YOUR VEHICLE.
Mazda gives a danger of explosion if the coin cell is not correct.

  1. Install the new coin cell in the same position as the used coin cell.
    • The marked face must be in the same direction as before.
    • Kia tells owners to make sure that the position of the coin cell is correct.
    <1m

Close the case of the key fob

Estimated under a minute

  1. Close the case.
    • Make sure that all parts of the case are together.
    • Make sure that no gap is between the two halves.
    <1m
  2. If your key fob has a mechanical key, install the mechanical key.
    <1m

Do a test of the key fob

Estimated 3 min to 6 min

  1. Move to a position near the vehicle.
    <1m
  2. Push the lock button on the key fob.
    <1m
  3. Make sure that the vehicle locks.
    <1m
  4. Push the unlock button on the key fob.
    <1m
  5. Make sure that the vehicle unlocks.
    • Do a test of each button on the key fob.
    <1m
  6. If the key fob does not operate, open the case again.
    • Examine the position and the direction of the new coin cell.
    • Examine the contacts in the holder for contamination.
    2m
  7. If the key fob does not operate after the second attempt, speak to the dealer for your vehicle.
    • Kia tells owners to speak to an authorized Kia dealer if they are not sure.
    <1m

Make the used coin cell safe

Estimated 3 min to 16 min

WARNING

DO NOT PUT A COIN CELL IN A FIRE.
DO NOT CRUSH A COIN CELL. Mazda gives these instructions because a coin cell can explode.

  1. Put the non-conductive tape on the two faces of the used coin cell.
    • CPSC tells you to put tape on the terminals immediately after removal.
    • Mazda gives the same instruction with cellophane tape or equivalent tape.
    <1m
  2. Keep the used coin cell away from children.
    <1m
  3. Take the used coin cell to a battery collection point.
    • CPSC tells you to discard a used coin cell at a battery collection center.
    2m
  4. Do not put a used coin cell in household waste.
    <1m

Terminology

This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.

key fob
Also called: car remote, remote, clicker, car key remote, keyless entry remote, smart key, transmitter, key thing, car fob
coin cell
Also called: button battery, button cell, watch battery, flat battery, round battery, CR2032, CR2025, little round battery, key fob battery
mechanical key
Also called: emergency key, valet key, hidden key, key blade, physical key, the metal bit inside the fob
operational range
Also called: range, distance it works from, how far away it works, signal range
type code
Also called: battery number, the number on the battery, battery code, battery size, type marking

When to use a professional

This procedure is for the coin cell in a key fob only. Do not use this procedure on the 12 V battery of the vehicle. Speak to a vehicle repair shop about the 12 V battery.

Mazda gives a recommendation to change the key battery at an authorized Mazda dealer. Kia tells owners to speak to an authorized Kia dealer if they are not sure about the replacement. If you are not sure, speak to the dealer for your vehicle.

Stop if the case of the key fob has damage. Stop if the circuit board has damage. Stop if the used coin cell has a leak. Speak to the dealer for your vehicle about a key fob with damage.

This procedure does not include a procedure to program a key fob. Speak to the dealer for your vehicle about a new key fob.

A swallowed coin cell is a medical emergency. Go to an emergency department immediately. CPSC tells you to call the National Battery Ingestion Hotline on 1-800-498-8666. CPSC also gives the Poison Help Line on 1-800-222-1222. CPSC tells you to take a child with a swallowed coin cell to the nearest emergency department immediately.

Common questions

What battery does my key fob take?

The honest answer is that this page cannot tell you, and any page that tells you without knowing your vehicle is guessing. Mazda's own manuals disagree across models: the 2018 CX-5 manual says to replace only with the same type battery, CR2025 or equivalent, and the 2025 CX-30 manual says CR2032 or equivalent. Kia's smart key page says CR2032, and Kia's Seltos manual calls the cell a 3 volt lithium battery. Those are three different documents for three different keys, which is exactly why the number belongs to your vehicle rather than to an internet page. Read the marking on the cell you are taking out and check it against the key section of your own owner's manual, and buy that.

My key fob only works when I am right next to the car. Is the battery dying?

Very probably. Mazda's manual lists three conditions that indicate the key battery power is low, and a reduced operational range for the system is one of them. The other two are the green KEY indicator light flashing in the instrument cluster, and the system not operating with no flash from the operation indicator light on the transmitter itself. A fob that works at arm's length but not across a car park is the classic version of the third symptom. It is a cheap thing to rule out before you assume the remote has failed.

Is a key fob battery actually dangerous?

The battery is the only genuinely dangerous part of this job, and the danger is to children rather than to you. The US Consumer Product Safety Commission states that a button cell battery can burn through a child's throat or esophagus in as little as two hours if swallowed, and that from 2011 through 2021 it was aware of 27 deaths and an estimated 54,300 emergency-room injuries associated with ingested or inserted button cell or coin batteries. Kia prints the same point in its own manual: if swallowed, a lithium button battery can cause severe or fatal injuries within 2 hours. Keep both the new cell and the old cell off the table and out of reach the whole time. If you think a child has swallowed one, CPSC says to seek immediate medical attention and to call the National Battery Ingestion Hotline on 1-800-498-8666 or the Poison Help Line on 1-800-222-1222.

Do I have to reprogram the fob after changing the battery?

The manufacturer documents read for this page do not ask for anything after the cell is changed. Kia's smart key battery page gives the replacement steps and then stops, with no reprogramming step and no mention of resynchronising the key. Mazda's page likewise ends at reassembly. That is two manufacturers, not all of them, so check the key section of your own manual rather than treating this as a general rule. If your fob does not respond after a correctly fitted new cell, the page routes you to your dealer instead of guessing at a button sequence.

Should I just let the dealer do it?

That is a legitimate choice and one manufacturer actively suggests it. Mazda's manual states that incorrect battery replacement operation may damage the key and that replacing the battery at an Authorized Mazda Dealer is recommended, and it only gives the DIY steps for owners who go ahead anyway. Kia says to contact an authorized Kia dealer if you are unsure how to use or replace the battery. The risk they are describing is a broken case or a damaged circuit board, not injury. If the fob is expensive to replace or the case looks fragile, paying someone is a reasonable trade.

What do I do with the old battery?

Do not leave it loose on a worktop and do not put it in the household bin. CPSC's advice is that as soon as a discharged cell is removed from a product you should place non-conductive tape, for example electrical tape, over the battery's terminals or around the entire battery, and discard it at a battery-collection center. Mazda's manual gives the same instruction in its own words, telling owners to insulate the plus and minus terminals of the battery using cellophane or equivalent tape, and never to disassemble the cell, throw it into fire or water, or deform or crush it. A used coin cell still holds enough charge to injure a child.

How long should a key fob battery last?

Kia's manual says the folding key or smart key uses a 3 volt lithium battery which will normally last for several years. That is the only service-life figure found in a first-party document during the research for this page, and it is a Kia statement about Kia keys rather than a general rule. Fobs that are used more often, or that sit next to a phone or a car and stay awake, will run down sooner. Treat the symptoms in the second question as the real signal rather than a date on a calendar.

Sources

Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.

  1. Tier 1How to Replace the Key Battery — 2025 Mazda CX-30 Owner's Manual, Key InspectionMazda North American Operations · accessed 2026-07-29 · re-verification due 2027-01-25
  2. Tier 1Warnings and Cautions about Key Battery Replacement — 2025 Mazda CX-30 Owner's Manual, Key InspectionMazda North American Operations · accessed 2026-07-29 · re-verification due 2027-01-25
  3. Tier 1Key Battery Replacement — 2018 Mazda CX-5 Owner's Manual, Owner MaintenanceMazda North American Operations · accessed 2026-07-29 · re-verification due 2027-01-25
  4. Tier 1Battery replacement — Smart key — Kia Owner's ManualKia · accessed 2026-07-29 · re-verification due 2027-01-25
  5. Tier 1Battery replacement — Kia Seltos Owner's Manual, KeysKia · accessed 2026-07-29 · re-verification due 2027-01-25
  6. Tier 1this product contains a button battery — Kia Owner's Manual, Battery replacementKia · accessed 2026-07-29 · re-verification due 2027-01-25
  7. Tier 1Button Cell and Coin Batteries — Safety Education CenterUnited States Consumer Product Safety Commission · accessed 2026-07-29 · re-verification due 2027-01-25
  8. Tier 1Making Families Safer from Button Cell or Coin Battery Dangers; Reese's Law Leads to New Federal Mandatory Safety StandardUnited States Consumer Product Safety Commission · accessed 2026-07-29 · re-verification due 2027-01-25

Revision history

Current version 4 · updated 2026-08-04 · next review due 2027-07-29

  1. v4 · 2026-08-04Corrected the attribution of the two-hour ingestion figure. The specification was named 'severe or fatal injury' and cited CPSC, but those are not CPSC's words: CPSC states that a swallowed button cell 'can burn through a child's throat or esophagus in as little as two hours'. The 'severe or fatal injuries within 2 hours' wording belongs to kia-button-battery-warning, a separate tier-1 source already in the registry. Both statements now publish under the source that made them, which also widens the population from lithium coin cells to every button cell, as CPSC has it. The page-level WARNING carries both sentences for the same reason.
  2. v3 · 2026-07-29The two emergency telephone numbers were added to the page-level WARNING itself, so that a reader who is holding a loose coin cell gets the number in the hazard block and not only in the professional boundary further down the page. The hazard level, the hazard placement and the consequence text are unchanged, and no step, specification or source changed. This entry is written to keep the revision log in step with the version number: reader checklist progress is keyed to the version, the version was raised for this change, and a version with no entry against it is how a later session loses the reason for an edit.
  3. v2 · 2026-07-29Emergency-routing review. No step, no hazard level, no hazard placement, no specification and no source changed, and both emergency telephone numbers stay on the page. Recorded because the numbers were briefly at risk of being dropped: a verification pass found that scripts/pii_scan.py reported the battery-ingestion hotline in this record as a finding, because at that moment config.json declared only the Poison Help line under site.public_numbers. The scanner reads a decision out of config rather than making one, so the two available fixes were to declare the hotline or to delete it from the page. It has since been declared in config, the scanner reports the tree clean, and the page keeps the number CPSC names first for a swallowed cell. This entry exists so that a later session that sees the hotline number here knows it is a declared public safety number and not an oversight, and does not silently delete it to clear a scanner line.
  4. v1 · 2026-07-29First draft. The value readers come for — the coin cell type — is per vehicle and publishes unverified as an instruction to read the marking on the used cell and to consult the vehicle documentation, under rule 1. Mazda's 2018 CX-5 manual (CR2025) and Mazda's 2025 CX-30 manual (CR2032) are published side by side as attributed per-model values to show that even one manufacturer gives two answers; that is per-unit variation and not a source conflict, so no conflict_note is recorded. The ingestion hazard rests on CPSC's Button Cell and Coin Battery Information Center and on Kia's own button battery warning, and it is the page-level WARNING. The explosion and circuit board hazards come from Mazda's warnings page. Disposal follows CPSC and Mazda. Honda's owner's manual pages could not be read and are recorded under rejected rather than cited.

Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.

Comments and corrections

Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.

Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.

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