Replace the Key Fob Battery

Last updated: June 12, 2026

If the smart key on your Hyundai Tucson Mk4 (NX4, 2020–present) is getting weak — short range, fussy keyless entry, or a “key battery low” message — the coin cell needs renewing. The Tucson’s smart key takes a CR2032 and opens with the hidden emergency blade. No programming needed; here’s how.

What You’ll Need

• A fresh CR2032 3 V lithium coin cell.
• The mechanical key inside the fob, plus a small flat screwdriver.

How to Replace the Tucson Mk4 Key Battery

1. Pull out the mechanical key blade — slide the release catch and withdraw it.
2. Use the slot the blade leaves (or the seam) and a small screwdriver to prise the case open.
3. Lift out the old CR2032, noting it sits positive side up.
4. Fit the new cell the same way, by the edges.
5. Click the case together and slide the blade home.
6. Test lock/unlock and keyless entry from a normal distance.

Does It Need Programming?

No — the swap doesn’t affect the key’s pairing, so it works straight away. A lost or extra smart key can only be ordered and coded by a Hyundai dealer.

If It Still Won’t Respond

Re-open the fob and check the cell sits positive-up with clean contacts. If keyless entry is slow, hold the smart key against the START button to start (Hyundai marks the spot), then it re-syncs.

Frequently Asked Questions

What battery does the Tucson Mk4 key take?

A single CR2032 3 V lithium coin cell.

Will the car start with a flat key battery?

Yes — hold the smart key against the START button to start on the backup transponder; the mechanical key unlocks the driver’s door.

Which way up does the cell go?

Positive (+) side up, matching the cell you removed.

Can I program a spare key myself?

No — Hyundai key coding needs the dealer system. Only the battery swap is DIY.

To clear a service reminder after maintenance, see our Tucson Mk4 service reset guide. For warning lights, look up the code on autodtcs.com.