These instructions apply to the Lexus LS Mk4 (USF40/UVF45) 2006-2017.
For other models, please choose your vehicle here.
If the smart key on your Lexus LS (2006–2017) 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 note the LS standard key takes a CR1632 (not the CR2032 many cars use), and the card-style key takes a CR2412. The fourth-generation LS (USF40/UVF45 platform) uses Lexus Smart Access proximity entry, so the key transmits a low-power signal whenever you’re near the car; that constant activity is why a fob cell wears down sooner than you’d think. A fading fob almost never means a fault with the car itself — it’s the coin cell, and you can change it in a couple of minutes.
How to Tell the Fob Battery Is Dying
A Smart Key cell fades rather than failing outright, so the warning signs creep in over a week or two:
- Shrinking range — you used to lock the LS from across the car park; now you almost have to touch it.
- A “key battery low” warning shows in the instrument display — the car’s clearest hint that the fob, not the vehicle, needs a fresh cell.
- Proximity entry only works up close — the handles stop unlocking on approach and you have to press the button or hold the fob to the handle.
- It works on the second or third press — a cell that can still deliver one strong burst but not repeat it.
- Worse in cold weather — coin cells drop voltage when chilled, so a marginal battery misbehaves on a frosty morning first.
As a rule of thumb, a button-only fob lasts three to four years, but a proximity Smart Key like the LS’s is usually nearer one to two years because it’s always listening for the car. If yours is a couple of years old and playing up, the cell is the first and cheapest thing to rule out.
The Battery You Need
- Standard smart key (with a pull-out mechanical key) — CR1632.
- Card-style smart key — CR2412.
Both are 3 volt lithium coin cells, but they are not interchangeable, and the LS standard key is the one to watch: it takes a CR1632, not the CR2032 that so many other cars use. The two look similar but the CR1632 is the thinner cell, so grabbing a CR2032 off the shelf out of habit will leave you with a battery that won’t seat properly. The safest move is to open the key first, read the code stamped on the cell you remove, then buy an exact match from a reputable brand. Never pad out a thinner cell to make it fit — it will lose contact and rattle loose.
If your key is dead right now you can still drive: hold the fob against the START button as you press it, and the mechanical blade in the standard key unlocks the driver’s door.
Replacing the Cell
Standard smart key:
- Push and hold the release knob and pull out the mechanical key. That blade is your backup — and removing it exposes the seam you’ll open next.
- Separate the two halves of the case with a small flat screwdriver at the seam where the key slid out. Ease around the joint rather than prying one point hard.
- Note which way the cell sits before you touch it — the printed + face is normally upward. Lift the old CR1632 out, handling it by the edges only.
- Fit the new CR1632 the same way up, positive side up. Double-check it’s a CR1632 and not a CR2032, wipe it with a dry cloth, and avoid touching the flat faces — skin oil raises contact resistance.
- Clip the case shut until it clicks all the way round, then refit the mechanical key.
Card key: pull off the cover, fit a new CR2412 positive side up, and refit. The card key has no mechanical blade, so keep a spare cell handy.
⚠️ Watch the polarity. A coin cell fitted upside down won’t work and can deform the holder’s contact spring. If the printed + faced up when you removed the old one, the new cell goes in exactly the same way.
Make Sure It Took
Stand a few metres back and lock, then unlock, watching the indicators flash to confirm range is restored. Walk up to the LS and try the proximity handles — with a healthy cell the doors should unlock as your hand reaches the handle. Press START to confirm the car reads the key normally. If a “key battery low” message was showing, it usually clears on its own after a drive cycle once the fresh cell is talking to the car.
If a Fresh Cell Doesn’t Help
- Re-check orientation and seating — the commonest cause is a cell that’s upside down or not fully clipped under the retaining tab.
- Confirm you fitted the right code — CR1632 for the standard key (not CR2032), CR2412 for the card key. A wrong-height cell makes weak contact.
- Wipe the contacts — a dry-cloth rub of the holder terminals clears any film or light corrosion.
- Use the backup start — hold the fob flat against the START button as you press; the car reads it by proximity even with a weak battery.
- Rule out the car’s 12 V battery — if the whole car is slow to wake and the dash flickers, the vehicle battery may be the real culprit.
- Still flagging? A smart-entry fault can store a diagnostic code — look it up on autodtcs.com.
New Key or Spare — Why It’s a Dealer Job
Changing the battery keeps all of the key’s existing coding, so nothing needs reprogramming afterwards. A new or replacement key is different: it has to be paired to your car’s VIN with diagnostic equipment, and there’s no owner button sequence for it. That’s a job for a Lexus dealer or an automotive locksmith. If you keep a spare key put away, change its CR1632 every few years too — the emergency key is exactly the one you’ll find flat when you finally reach for it.
Frequently Asked Questions
What battery does the Lexus LS key use?
The standard Smart Key with the pull-out mechanical blade takes a CR1632 3 V lithium coin cell — note that’s CR1632, not the CR2032 many other cars use. The card-style Smart Key takes a CR2412. Read the code on the old cell before buying, as they are not interchangeable.
Which way up does the coin cell go?
Positive side up in both key types — the printed + face should show after you seat it. Before removing the old cell, note how it sits and fit the new one identically. A cell placed upside down will not power the fob.
Do I need to reprogram the key after the swap?
No. A battery change retains all the existing coding, so the key works immediately once the fresh cell is in and the case is clipped shut. Reprogramming is only needed for a brand-new or replacement key that has never been paired to your LS.
How long should the new battery last?
Because the LS uses proximity entry, the Smart Key is always transmitting, so expect roughly one to two years from a standard fob cell — less than a button-only key. If it drains much faster, make sure the fob isn’t stored next to another transmitter that keeps it awake.
The key still doesn’t work with a new cell — now what?
First confirm you fitted a CR1632 and not a CR2032, then re-check polarity and seating and wipe the contacts. If the car is also slow to wake, suspect the 12 V vehicle battery rather than the fob. A persistent smart-entry fault may log a code you can research on autodtcs.com.
Can I drive if the fob battery is completely dead?
Yes. Use the mechanical blade inside the standard key to unlock the driver’s door, then hold the fob flat against the START button as you press it — the car reads the key by close proximity even with a flat coin cell, so you can drive to buy a replacement.
If the key flagged low after a battery disconnection, see our LS battery disconnect/reconnect guide, and to decode any warning that lingers, use autodtcs.com.
Independent guide — not affiliated with Lexus. Always follow your official service manual and safety precautions. Read our full disclaimer.