Dead Key Fob Battery medium urgency

2024 Toyota Prius Dead Key Fob Battery (US): How to Unlock & Start Your Car

A dead key fob battery on a 2024 Toyota Prius can stop remote lock/unlock and may prevent the car from detecting the fob for push-button start. The good news: you can still get in and start the Prius using the built-in mechanical key and the fob’s emergency start procedure. Replacing the fob battery is usually quick and inexpensive.

Understanding Your Situation

The small coin-cell battery inside the Prius smart key has depleted, so the fob can’t transmit a strong signal for remote functions or reliable proximity detection. The fob still contains a mechanical key for the driver’s door, and the vehicle has a backup method to read the fob at close range so you can start the car.

🚀 Immediate Steps to Take

  1. Unlock the driver’s door with the hidden mechanical key (release it from the fob and use the key cylinder on the driver’s door handle).
  2. Start the Prius using the backup method: hold the Toyota emblem side of the fob directly against the POWER button (or as close as possible), then press the brake and press POWER to start.
  3. Replace the fob battery with a new coin-cell of the same type as your original (commonly CR2032 on many Toyota smart keys—verify the marking inside your fob), then test lock/unlock and starting.

Your Options

DIY coin-cell battery replacement

Cost: $3-$10 Time: Same day

Open the smart key fob, remove the old coin-cell battery, install a new battery of the same type with correct polarity, and reassemble the fob. Then confirm remote functions and that the car detects the fob normally.

âś“ Pros:
  • Lowest cost
  • Fast fix with common batteries available at most stores
âś— Cons:
  • Small parts can be easy to lose or damage
  • Using the wrong battery type or installing it backward won’t solve the problem

Battery replacement at a Toyota dealer or independent shop

Cost: $10-$30 Time: Same day

A service advisor or technician replaces the coin-cell and verifies the fob works. Useful if you’re unsure how to open the fob or want confirmation it’s not a different issue.

âś“ Pros:
  • Professional help and quick verification
  • Reduces risk of breaking the fob housing or seals
âś— Cons:
  • Higher cost than DIY
  • May require a short wait or appointment

Mobile locksmith or roadside assistance (if you’re stuck)

Cost: $75-$200 Time: Same day

If you can’t unlock the car or start it with the backup method, a mobile locksmith or roadside provider can help you gain entry and confirm whether the issue is the fob battery, the fob itself, or a vehicle-side problem.

âś“ Pros:
  • Help comes to your location
  • Good option if you’re stranded away from home
âś— Cons:
  • More expensive than a simple battery swap
  • Quality and capability vary by provider

⚠️ What to Avoid

✕ Forcing the fob open with excessive pressure or metal tools that can crack the housing or damage internal components—use gentle prying at the designated seam.

✕ Installing a different battery size/chemistry or mixing old/new batteries—use one new coin-cell of the exact type printed inside the fob.

✕ Assuming it’s always the fob battery: if the car still won’t start with the fob held against the POWER button, the issue could be the vehicle’s 12V battery, a damaged fob, or interference.

Frequently Asked Questions

Can I still start my 2024 Toyota Prius 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 directly against/next to the POWER button while pressing the brake and pressing POWER. This allows the car to detect the fob at very close range even if the fob battery is weak or dead.

What battery does the 2024 Prius key fob use?

Many Toyota smart keys use a CR2032 coin-cell, but you should confirm by opening your fob and reading the battery marking inside (the exact type can vary by fob version). Replace it with the same type and install it with the correct polarity.

My Prius remote buttons don’t work, but the car still starts—does that mean the battery is low?

Often, yes. Remote lock/unlock typically stops working before the car completely stops detecting the fob for starting. Replace the coin-cell soon to avoid getting stuck using the backup procedure.

After replacing the battery, do I need to reprogram the key fob?

Usually no. A battery replacement should not erase programming. If the fob still doesn’t work afterward, recheck battery type/polarity and ensure the contacts are clean and seated; if problems continue, the fob may be damaged or the issue may be with the vehicle.

⏱️ Urgency Note: Low to moderate urgency: you can typically unlock and start the Prius using the mechanical key and backup start method, but replace the fob battery promptly to avoid being stranded—especially before travel or in bad weather.

Related Information

Need Detailed Information?

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

View Prius Key Fob Guide →

Last updated: 2026-01-04