Replace the Key Fob Battery

Last updated: June 8, 2026

If the smart key on your Lexus ES 300h (2018–present) has lost its range or shows a low-key-battery message, the coin cell inside is almost certainly flat. It’s a quick swap — just check which key type you have.

Battery First — Two Key Types

• Standard smart key (with a pull-out mechanical key) — CR2032.
• Card-style smart key — CR2412 (check before buying).

If the key is dead you can still start the car: hold it against the START button as you press it. The mechanical blade in the standard key unlocks the driver’s door.

Replacing the Cell

Standard smart key:

1. Push and hold the release knob and pull out the mechanical key.
2. Separate the two halves of the case with a small screwdriver at the seam.
3. Lift out the old cell (don’t touch the terminals) and fit a new CR2032, positive side up.
4. Close the case and refit the mechanical key.

Card key: pull off the cover, fit a new CR2412 positive side up, and refit.

Lost Key or Adding a Spare

A cell swap keeps the existing coding. A new key must be programmed by a Lexus dealer with diagnostic equipment — there’s no owner sequence.

If a Fresh Cell Doesn’t Help

• Confirm the cell type and orientation (CR2032 standard, CR2412 card, positive up).
• Hold the key to the START button to drive in the meantime.
• Still flagging? A smart-entry fault can store a code — look it up on autodtcs.com.

Frequently Asked Questions

What battery does the Lexus ES key use?

A CR2032 in the standard smart key, or a CR2412 in the card-style key.

Do I need to reprogram the key after the swap?

No — the coding is retained for a battery change.

Can I program a new ES key myself?

No — a new key must be coded by a Lexus dealer.

The key is dead — how do I start the car?

Hold the key against the START button as you press it.

For more reset and maintenance how-tos, see our other Lexus guides.