These instructions apply to the Lexus RX Mk4 (AL20) 2015-2022. For other models, please choose your vehicle here.
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Disconnecting the 12 V battery on your Lexus RX (2015–2022) — for a new battery, winter storage, or work near the airbags — catches owners out, because on this car the 12 V isn’t under the bonnet, it’s in the boot.
Find the 12 V Battery First
On the RX 450h hybrid the 12 V battery is in the luggage compartment — lift the boot carpet/trim to reach it. The under-bonnet terminals are for jump-starting only. This 12 V battery is the one you service; never touch the orange high-voltage cabling or the hybrid battery. On the petrol RX 200t/300 the battery is in the engine bay.
Disconnecting Safely
- Switch off and make sure all electrical consumers are off.
- Lift the boot floor/trim to reach the battery, then disconnect the negative (−) terminal first, then the positive.
- Working near airbags or pretensioners? Wait 90 seconds after disconnecting before such work.
Reconnecting and Re-initialising
Reconnect positive first, then negative. The RX then relearns a few items as you drive:
- Steering angle / stability and parking-assist systems relearn as you drive straight and turn fully each way.
- Power windows and tailgate — if one-touch is lost, re-initialise (pull-up-and-hold the window at the top; the power tailgate relearns its travel).
- Re-enter the clock, presets and settings.
If Something Isn’t Right Afterwards
- Warning lights (e.g. VSC/stability) usually clear once the relearns complete after a short drive.
- 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 luggage compartment (boot), under the floor/trim — the under-bonnet terminals are only for jump-starting.
Is it safe to disconnect the 12 V on the hybrid?
Yes — the 12 V is separate from the high-voltage system; never touch the orange HV cabling.
Which terminal first?
Negative (−) off first, reconnect it last.
What needs resetting afterwards?
Steering-angle/stability and parking-assist relearn by driving; windows and tailgate may need a relearn; plus the clock and presets.
If a warning light stays on after reconnecting, look up the code on autodtcs.com.
Disclaimer: The information on this page is provided for general guidance only. Always follow your official service manual and safety precautions when working on your vehicle. We are not responsible for errors, omissions, or any damage resulting from the use of this information.
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