Replace Key Battery medium urgency

2024 Mazda CX-5 Dead Key Fob Battery (US): How to Unlock & Start Your Car

If your 2024 Mazda CX-5 key fob suddenly won’t lock/unlock the doors or the car says the key isn’t detected, the most common cause is a dead (or weak) fob battery. The good news: you can still get in and start the vehicle using the built-in emergency methods.

Understanding Your Situation

The keyless entry and push-button start rely on a small coin-cell battery inside the fob. When it’s weak or dead, the fob can’t transmit a strong signal, so the CX-5 may not unlock remotely or recognize the key unless you use the backup start procedure.

🚀 Immediate Steps to Take

  1. Unlock the driver’s door with the hidden mechanical key: slide the release on the fob to remove the emergency key, then use it in the door lock (remove the small cover/cap on the handle if equipped).
  2. Start the CX-5 using the backup method: hold the Mazda emblem side of the fob against the START/STOP button (or place it right next to the button) and press the brake, then press START/STOP to start.
  3. Replace the fob battery as soon as possible (typically a CR2032 coin cell for Mazda fobs, but confirm by checking your owner’s manual or the battery marking inside the fob).

Your Options

Replace the key fob battery yourself (DIY coin-cell swap)

Cost: $3-$12 Time: Same day

Open the fob case, remove the old coin-cell battery, and install a new one with the correct orientation. Test lock/unlock and starting afterward.

âś“ Pros:
  • Fast and inexpensive
  • No programming required for a simple battery replacement
âś— Cons:
  • Risk of damaging the fob case or seal if pried incorrectly
  • Wrong battery type or upside-down installation can mimic a bad fob

Battery replacement at a dealer or automotive locksmith

Cost: $10-$40 Time: Same day

A dealer service department or locksmith replaces the coin cell and confirms the fob works (lock/unlock and start).

âś“ Pros:
  • Reduced chance of breaking the fob housing
  • Quick confirmation if the issue is more than the battery
âś— Cons:
  • Higher cost than DIY
  • May require travel/towing if you can’t access the vehicle or start it

If it still won’t work: diagnose fob/vehicle issue (spare key test)

Cost: $0-$250+ Time: Same day / 1-3 days

Try a spare fob (if available). If the spare works, the original fob may be damaged. If neither works, the vehicle may have a receiver issue or there may be interference. A dealer or locksmith can diagnose and replace/repair as needed.

âś“ Pros:
  • Helps confirm whether it’s the fob or the vehicle
  • Prevents unnecessary parts replacement
âś— Cons:
  • Diagnosis may take time
  • Repairs beyond the battery can be costly

⚠️ What to Avoid

✕ Don’t force the fob open with excessive prying—use gentle pressure to avoid cracking the case or damaging internal clips.

✕ Don’t install a different battery type/size “because it fits”—use the exact coin-cell model specified (commonly CR2032, but verify).

✕ Don’t keep repeatedly pressing the fob buttons for long periods—this can overheat a failing battery and won’t fix a no-signal condition.

⚠️ Common Mistakes to Avoid

  • Using wrong battery type
  • Damaging case during opening
  • Not resetting after replacement
  • Buying expensive batteries

Frequently Asked Questions

Can I start my 2024 Mazda CX-5 if the key fob battery is dead?

Yes. Use the mechanical key to get in, then use the backup start method by holding the fob against/near the START/STOP button and pressing the button while holding the brake. The vehicle can read the fob’s transponder at close range even if the fob battery is dead.

What battery does a 2024 Mazda CX-5 key fob use?

Many Mazda key fobs use a CR2032 coin-cell battery, but you should confirm by checking your owner’s manual or the battery marking inside the fob before buying.

Will I lose programming if I change the key fob battery?

No. Replacing the coin-cell battery does not erase key programming. If the fob still won’t work after a correct battery swap, the fob may be damaged or there may be a vehicle-side issue.

Why does the car say “Key Not Detected” even with a new battery?

Common causes include the battery installed upside down, poor contact with the battery terminals, a damaged fob (water drop/impact), radio interference, or a vehicle receiver/antenna issue. Try the spare fob and the backup start method to narrow it down.

⏱️ Urgency Note: Moderate urgency: you can usually still unlock and start the CX-5 using the backup methods, but replace the battery soon to avoid being locked out later or stranded if you don’t have the mechanical key accessible.

Related Information

Need Detailed Information?

Get vehicle-specific key fob compatibility, part numbers, and a complete price comparison for your 2024 Mazda CX-5.

View CX-5 Key Fob Guide →

Last updated: 2026-01-04