These instructions apply to the Lexus RX Mk1 (XU10) 1998-2003.
For other models, please choose your vehicle here.
The first-generation Lexus RX 300 (XU10, 1998–2003) came from an era before push-button smart keys, so its remote is a small, separate keyless-entry fob that lives on the same ring as an ordinary cut metal ignition key — not a one-piece smart key. Press lock or unlock and nothing happens, or you have to be almost touching the car? That is the classic sign the little lithium coin cell inside the remote has gone flat. Some cars in this run instead carry a “remote head” key, where the same lock/unlock buttons are built into the fat plastic head of the metal key; both open in much the same way and take the same battery. Here is how to tell a dying cell from a real fault, the exact battery to buy, and how to swap it in a couple of minutes.
How to Tell the Fob Battery Is Dying
- Shrinking range. You used to lock the RX from across the car park; now you have to stand right beside it. Fading range is almost always the first symptom of a tired cell.
- The LED barely lights, or not at all. The remote’s little indicator light dims or stops flashing on a button press once the cell voltage drops — a quick way to confirm it is the fob, not the car.
- Works only sometimes. Intermittent locking, especially in cold weather, is a near-flat cell that cannot deliver the brief burst of current the transmitter needs.
- No dashboard warning. This generation is too early to show a “key battery low” message in the cluster — unlike modern Lexus models, the XU10 gives you no dash alert, so you are watching range and the LED instead.
A coin cell in an RX 300 remote typically lasts two to four years. If yours is older than that and showing any of the above, fit a fresh cell before you start suspecting the door receiver.
The Battery You Need
The RX 300 remote uses a CR1616 3-volt lithium coin cell — the same small cell Lexus fitted across its late-1990s and early-2000s range (ES 300, GS 300, LX 470, Land Cruiser and more). It is 16 mm across and just 1.6 mm thick, so it is noticeably thinner than the common CR2032 — do not substitute a thicker cell that merely fits the diameter. A few aftermarket remote-head keys for this car have been listed with a CR2016 instead, so the golden rule is simple: open the fob first and read the code printed on the cell you remove, then buy that exact one. Choose a good branded lithium cell; cheap ones sag under load and can give short range even when “new”.
Method 1 — Separate Keyless-Entry Remote
- Take the small remote off the key ring so you can hold it steady and see the seam that runs around its edge.
- Wrap the tip of a small flat-blade screwdriver in a strip of tape to avoid marking the case, then insert it into the seam and gently twist to split the two halves apart. Work your way around rather than forcing one spot.
- Note which way the old cell sits — take a photo if in doubt — then lift it out. Read the printed code (CR1616) to confirm the replacement.
- Drop the fresh cell in the same orientation you removed the old one. On these Lexus remotes the positive (+) face is usually uppermost, but always copy what you found.
- Press the halves back together until the seam clicks shut all the way round, and test every button.
Method 2 — Remote-Head Key Variant
- If your car uses the one-piece remote-head key, look for a fine seam around the plastic head where the buttons live.
- Insert a taped flat-blade screwdriver into that seam and ease the head apart to expose the battery. There is no separate screw on these keys.
- Lift out the old cell, check its printed code (usually CR1616, occasionally CR2016) and match it.
- Fit the new cell the same way up, close the head firmly until it clicks, and test the buttons.
⚠️ Match the polarity you found. Fitting the cell upside down will not let the remote transmit and can slowly discharge the new battery — so before you close the case, double-check the new cell sits exactly as the old one did.
Did It Work?
Stand a few metres back and lock, then unlock, the RX. Full range should return straight away and the LED should flash brightly on each press. If it does, you are done — there is nothing to reprogram after a simple battery change on this generation.
If a Fresh Cell Doesn’t Fix It
- Re-check the orientation and seating. A cell fitted the wrong way up, or not clipped firmly against both contacts, is the most common reason a “new” battery does nothing.
- Clean the contacts. Finger grease or light corrosion on the metal terminals is enough to cause dropouts — wipe them with a dry cloth.
- Confirm the cell size. A CR1616 and a CR2016 look similar but differ in thickness; the wrong one can sit proud of the contacts and misbehave. Verify against the code you removed.
- Suspect the transmitter. If the LED still will not light with a known-good cell, the remote’s electronics may have failed — common on a 20-plus-year-old fob — and it would need replacing and pairing.
New Key or Spare — Why It’s a Dealer or Locksmith Job
Changing the coin cell keeps the remote’s existing coding, so no reprogramming is needed. A new remote or key is a different matter: the RX 300’s immobiliser transponder has to be programmed to the car, and the remote itself paired to the door receiver — work that needs the correct equipment and, for the transponder, the car present. On a vehicle this age, a good auto-locksmith is often quicker and cheaper than a Lexus dealer for cutting and coding a spare, so it is worth keeping a second working key rather than being left with just one.
Frequently Asked Questions
What battery does a Lexus RX 300 (1998–2003) remote take?
A CR1616 3-volt lithium coin cell in almost all cases. A small number of aftermarket remote-head keys have used a CR2016, so open the fob and buy whatever code is printed on the cell you remove.
Which way up does the cell go?
Fit it the same way the old one came out — on these Lexus remotes the positive (+) side usually faces up. Copying the original orientation avoids a non-working or slowly draining battery.
Do I need to reprogram the remote after changing the battery?
No. A battery swap does not affect the coding, so the remote works the moment you close it back up. Only a brand-new remote or key needs pairing and immobiliser programming.
Can I still start the RX if the remote battery is dead?
Yes. On this generation the coin cell only powers the remote locking. The immobiliser chip inside the ignition key is passive — it draws no power from the coin cell — so a flat fob battery never stops the car starting. Just unlock the door with the metal key and turn the ignition as normal.
How long should the remote battery last?
Usually two to four years. Frequent locking and unlocking, or a slightly weak old cell, will shorten that.
My remote still won’t work after a new battery — what now?
Re-check polarity, seating and that you used the correct cell size, then clean the contacts. If the LED still will not light with a fresh, known-good cell, the transmitter has likely failed and the remote needs replacing — not unusual on a fob of this age.
If the doors started misbehaving right after the car’s 12 V battery was disconnected or went flat — rather than the remote fading gradually — the cause may be a stored body or immobiliser fault rather than the coin cell; you can look up what a logged code means on autodtcs.com.
Independent guide — not affiliated with Lexus. Always follow your official service manual and safety precautions. Read our full disclaimer.