These instructions apply to the Lexus RX Mk3 (AL10) 2009-2015.
For other models, please choose your vehicle here.
Disconnecting the 12 V battery on your Lexus RX (2009–2015) — the AL10 — for a new battery, winter storage, or work near the airbags catches owners out on the hybrid, because on the RX 450h the 12 V isn’t under the bonnet, it’s in the boot.
Owners disconnect the 12 V battery on the AL10 RX for the usual reasons — fitting a replacement, laying the car up for the winter so a slow drain can’t flatten it, doing electrical repairs, or working safely near the airbags and pretensioners. The important thing to understand on this car is that it comes in two very different forms. The RX 450h is a hybrid: it has a small 12 V battery for the ordinary electronics and a completely separate high-voltage traction battery for the electric drive. You only ever touch the 12 V battery. The high-voltage system is identified by its orange cabling and is off-limits — leave it strictly alone. The RX 350 is a conventional petrol V6 with a normal under-bonnet battery. Do the 12 V job in the right order and the car relearns cleanly.
Where the 12 V Battery Is
- RX 450h (hybrid): the 12 V battery is in the luggage compartment (boot), under the floor/trim. The under-bonnet terminals are for jump-starting only. Never touch the orange high-voltage cabling.
- RX 350 (petrol): the battery is in the engine bay, conventional location.
On either version the battery has the same two posts: the negative (−) with a black lead and body earth, and the positive (+) under a red cover. Identify them before you start.
First, a Few Checks
- Make sure the car is fully off and not in READY mode — on the 450h, check the READY light is out before you go near the battery.
- Take the smart key well away from the car so it can’t wake the system.
- Switch off the lights, climate control and audio, and close the tailgate settings you were using.
- Note your radio presets and have any audio security code ready.
- Give it a couple of minutes with everything off so the modules power down, and have gloves, eye protection and the right spanner to hand.
Disconnecting Safely
- Switch everything off and confirm READY is out and the key is away.
- Disconnect the negative (−) terminal first, then move the lead clear of the post.
- Now disconnect the positive (+) terminal.
- Working near airbags or pretensioners? Wait 90 seconds after disconnecting before such work.
Reconnecting and Re-initialising
Reconnect in reverse: positive (+) first, then the negative (−) last, and tighten both clamps securely. The RX then relearns a few items as you drive:
- Steering angle / stability relearn as you drive straight and turn fully each way.
- Power windows — if one-touch is lost, pull-up-and-hold at the top to relearn.
- Re-enter the clock, presets and settings.
If Something Isn’t Right Afterwards
- Check both clamps are properly tight — the most common cause of odd behaviour after a battery job is a loose terminal.
- Warning lights such as VSC usually clear after a short drive once the relearns complete.
- If the one-touch windows still misbehave, repeat the pull-up-and-hold relearn.
- A persistent light stores a code — look it up on autodtcs.com.
- Fit a like-for-like aux battery (the 450h uses a specific small AGM-type).
Frequently Asked Questions
Where is the 12 V battery on a Lexus RX 450h?
In the boot (luggage compartment), under the floor/trim — the under-bonnet terminals are only for jump-starting. The 450h is a hybrid, so its small 12 V battery is separate from the high-voltage traction battery.
And on the RX 350?
In the engine bay, in the conventional location under the bonnet. The 350 is a normal petrol V6, so it has an ordinary under-bonnet 12 V battery rather than a boot-mounted one.
Which terminal do I disconnect first?
Negative (−) off first, reconnect it last. On refitting, the positive (+) goes on first and the negative last. This keeps you from shorting a live positive post while you work.
Is it safe to work on the 12 V battery of the hybrid?
Yes — the 12 V battery is owner-safe on the 450h, just like any car battery. What you must never touch is the orange high-voltage cabling and the traction battery. Confirm READY is out, then work only on the 12 V terminals.
What needs resetting afterwards?
The steering-angle and stability systems relearn as you drive, the power windows may need their one-touch re-initialising, and you’ll re-enter the clock, presets and settings. Any transient warning lights should clear after a short drive.
Does the aux battery need coding on the RX?
A like-for-like 12 V aux battery is a straight swap and doesn’t need coding. Just fit the correct specific small AGM-type unit the 450h uses, tighten the clamps and reset your presets — there’s no registration step for the owner.
If a warning light stays on after reconnecting, look up the code on autodtcs.com.
Independent guide — not affiliated with Lexus. Always follow your official service manual and safety precautions. Read our full disclaimer.