Dead Key Fob Battery medium urgency

2024 Hyundai Elantra Dead Key Fob Battery (US): How to Start, Unlock, and Replace It

If your 2024 Hyundai Elantra key fob suddenly won’t lock/unlock the doors or the car won’t detect the fob, the most common cause is a dead fob battery. The good news: you can still get in and start the car using the hidden mechanical key and the vehicle’s backup start method.

Understanding Your Situation

The coin-cell battery inside the smart key/remote has dropped too low to power the transmitter, so the car may not receive lock/unlock signals and may show “Key not detected.” The fob’s internal emergency key still works for the door, and the car has a backup way to recognize the fob for starting.

🚀 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 driver door key cylinder (remove the small cover if equipped).
  2. Start the car using the backup method: hold the fob right up to the START/STOP button (or the marked sensing area) and press the brake, then press START. This lets the car read the fob even with a weak/dead battery.
  3. Replace the fob battery as soon as possible: open the fob case carefully and install a new coin-cell battery of the correct type, matching the +/− orientation. Test lock/unlock and starting afterward.

Your Options

DIY key fob battery replacement (coin-cell)

Cost: $3-$12 Time: Same day (5-15 minutes)

Open the key fob case, remove the old coin-cell battery, and install a new one of the correct type. Reassemble the fob and verify lock/unlock and start functions.

✓ Pros:
  • Lowest cost
  • Fast and convenient
✗ Cons:
  • Opening the case improperly can crack the shell or damage clips
  • Using the wrong battery type or installing it backward will not fix the issue

Battery replacement at a parts store or retailer

Cost: $5-$20 Time: Same day

Buy the correct coin-cell battery and have a store associate install it (availability varies by retailer).

✓ Pros:
  • No tools or prying needed on your end
  • Quick confirmation the issue was just the battery
✗ Cons:
  • Not all stores install batteries or handle every fob style
  • Limited help if the fob has internal damage beyond the battery

Dealer service visit (battery + key check)

Cost: $0-$40 Time: Same day / 1-3 days (depending on appointments)

A Hyundai dealer replaces the battery and can check for other issues (fob damage, vehicle-side detection concerns) if the problem persists.

✓ Pros:
  • Correct battery and proper installation
  • Can diagnose if the problem isn’t the battery
✗ Cons:
  • May require an appointment and travel time
  • Higher cost than DIY in many cases

Replace the key fob (if battery doesn’t fix it)

Cost: $250-$550 Time: Same day / 1-7 days (if ordering parts)

If the fob is damaged or not transmitting, you may need a new OEM smart key and programming. This is not typically required for a simple dead battery, but it’s the next step if symptoms continue after a fresh battery.

✓ Pros:
  • Restores full reliability if the fob electronics have failed
  • OEM fit and function
✗ Cons:
  • Significantly more expensive than a battery
  • Programming may require dealer equipment and proof of ownership

⚠️ What to Avoid

✕ Don’t force the fob open with excessive prying—use the seam/slot and gentle pressure to avoid cracking the housing or breaking clips.

✕ Don’t use a “near size” coin-cell battery or stack batteries; install the exact type and ensure correct polarity (+/−).

✕ Don’t assume it’s the car battery right away—if the vehicle starts normally once the fob is held to the start button, the issue is usually the fob battery.

Frequently Asked Questions

Can I start my 2024 Hyundai Elantra if the key fob battery is dead?

Yes. Use the hidden mechanical key to unlock the door if needed, then use the backup start method by holding the fob against the START/STOP button (or sensing area) while pressing the brake and pressing START. The car can often read the fob’s transponder at close range even with a dead coin-cell.

What battery does the 2024 Elantra key fob use?

Most Hyundai smart keys use a coin-cell battery (commonly CR2032), but it can vary by fob design and trim. Check the marking on the old battery or your owner’s manual to confirm the exact type before buying a replacement.

Do I need to reprogram the key fob after replacing the battery?

Usually no. A battery replacement should not erase programming. If the fob still doesn’t work after a new battery, double-check battery orientation, confirm the battery is fresh, and inspect for corrosion or damage—then consider dealer or locksmith diagnosis.

Why does the door unlock with the key but remote buttons don’t work?

The mechanical key operates the physical lock and doesn’t rely on the fob battery. The remote lock/unlock and proximity functions require battery power, so they often fail first when the coin-cell is weak or dead.

⏱️ Urgency Note: Low safety urgency, but replace the battery soon—especially before travel. A dead fob battery can leave you using the mechanical key and backup start method, and repeated failures can be inconvenient in bad weather or unfamiliar areas.

Related Information

Need Detailed Information?

Get vehicle-specific key fob compatibility, part numbers, and a complete price comparison for your 2024 Hyundai Elantra.

View Elantra Key Fob Guide →

Last updated: 2026-01-04