2018 RX450hL auxillary battery replacement
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From: WI
2018 RX450hL auxillary battery replacement
It is seven years old and measures about 12.1V, so I think it may be time to replace it. Worth trying to desulphate it?
But basically looking for some guidance on the auxiliary battery replacement. It appears to be different from the 450h models probably because of the 3rd row seating. it is rotated 90 degrees and very close the rear quarter panel.
Two questions:
1) Will a size 47 fit? Or should I go with the 35?
2) How to undo the nut that holds the bracket down, it is not accessible easily compared to the 450h in videos I have seen.
Thanks!
But basically looking for some guidance on the auxiliary battery replacement. It appears to be different from the 450h models probably because of the 3rd row seating. it is rotated 90 degrees and very close the rear quarter panel.
Two questions:
1) Will a size 47 fit? Or should I go with the 35?
2) How to undo the nut that holds the bracket down, it is not accessible easily compared to the 450h in videos I have seen.
Thanks!
Last edited by tvarghese; Mar 14, 2025 at 04:09 PM.
Instructor
Joined: Feb 2021
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From: PA
But anyways to answer the OP's question, it calls for Group 47.
https://costco.interstatebatteries.c...option=2463394
Driver School Candidate
Joined: Jul 2022
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From: California
You've likely solved this problem but wanted to post here in case anyone from the future decides to search.
The 450hL 12V battery is not commonly available at most auto parts stores (Auto Zone, O'Reilly's, Napa, Costco, etc.). You'll likely have to go to Lexus to get a replacement battery because it's a special Japanese format. If you're in a bind (middle of nowhere) and a normal H5 AGM is your only hope, I'm sure the electronics will work--it's just that the H5 won't fit nicely back into the rear corner without rattling and/or cutting some of the bottom bracket. The vent tubes from a 450hL also don't fit an H5 AGM battery.
The 450h does use an H5 AGM but I think the 3rd row seats require a smaller battery in the 450hL.
The 450hL 12V battery is not commonly available at most auto parts stores (Auto Zone, O'Reilly's, Napa, Costco, etc.). You'll likely have to go to Lexus to get a replacement battery because it's a special Japanese format. If you're in a bind (middle of nowhere) and a normal H5 AGM is your only hope, I'm sure the electronics will work--it's just that the H5 won't fit nicely back into the rear corner without rattling and/or cutting some of the bottom bracket. The vent tubes from a 450hL also don't fit an H5 AGM battery.
The 450h does use an H5 AGM but I think the 3rd row seats require a smaller battery in the 450hL.
It is seven years old and measures about 12.1V, so I think it may be time to replace it. Worth trying to desulphate it?
But basically looking for some guidance on the auxiliary battery replacement. It appears to be different from the 450h models probably because of the 3rd row seating. it is rotated 90 degrees and very close the rear quarter panel.
Two questions:
1) Will a size 47 fit? Or should I go with the 35?
2) How to undo the nut that holds the bracket down, it is not accessible easily compared to the 450h in videos I have seen.
Thanks!
But basically looking for some guidance on the auxiliary battery replacement. It appears to be different from the 450h models probably because of the 3rd row seating. it is rotated 90 degrees and very close the rear quarter panel.
Two questions:
1) Will a size 47 fit? Or should I go with the 35?
2) How to undo the nut that holds the bracket down, it is not accessible easily compared to the 450h in videos I have seen.
Thanks!
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From: WI
Made some modifications to the holding bracket
Thanks for your response. I wound up with a slightly larger battery that has more power. It did not quite fit, so I had to make some adjustments to the bracket that held it in place. Yes, had to use a largish hammer to bend the metal into the size it needed it to be.
Went to ACE and got a barb that fit into the battery I bought. Sealed the sides with some silicone.
But it works so I'm going to leave it alone for the next 5 years or so and make any adjustments that I need to at that time.
Went to ACE and got a barb that fit into the battery I bought. Sealed the sides with some silicone.
But it works so I'm going to leave it alone for the next 5 years or so and make any adjustments that I need to at that time.
Last edited by tvarghese; Dec 20, 2025 at 05:12 AM.
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Thanks for your response. I wound up with a slightly larger battery that has more power. It did not quite fit, so I had to make some adjustments to the bracket that held it in place. Yes, had to use a largish hammer to bend the metal into the size it needed it to be.
Went to ACE and got a barb that fit into the battery I bought. Sealed the sides with some silicone.
But it works so I'm going to leave it alone for the next 5 years or so and make any adjustments that I need to at that time.
Went to ACE and got a barb that fit into the battery I bought. Sealed the sides with some silicone.
But it works so I'm going to leave it alone for the next 5 years or so and make any adjustments that I need to at that time.
I like to know exactly what battery you replaced and how you did connect the vent hose to the new battery.
Thanks in advance for your useful information.
4th Gear
Joined: Jan 2026
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Yeah, the L model battery setup is definitely tighter. You'll want the Group 35 battery, not the 47. The 47 is for the standard length RX. For that nut, a small socket wrench with a universal joint or a flex-head ratchet is your best bet to get in there at an angle.
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