Disconnect and Reconnect the Battery

Reviewed by the Service Reset editor · Updated August 9, 2026 · How we verify
Quick referenceTools10 mm spannerTime~15 minMethodDisconnect negative terminal first

These instructions apply to the Lexus RX Mk4 (AL20) 2015-2022.
For other models, please choose your vehicle here.

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.

Lexus RX Mk4 — the vehicle covered in this guide.
Lexus RX Mk4. Photo by Dinkun Chen via Wikimedia Commons, licensed CC BY-SA 4.0.

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

  1. Switch off and make sure all electrical consumers are off.
  2. Lift the boot floor/trim to reach the battery, then disconnect the negative (−) terminal first, then the positive.
  3. 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.

Independent guide — not affiliated with Lexus. Always follow your official service manual and safety precautions. Read our full disclaimer.

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