midcow3

Any metal on the frame or engine or engine compartment with the hood up is where you connect the black cable. In most cases, you want to avoid the battery in case there is a problem with the battery itself. Sometimes in extreme cases you completely disconnect the red wire (positive) from the battery and connect your positive (red) jumper to the red cable that was on the battery and ground the black cable as mentioned above. This completely takes the 12 Volt battery out of the electrical circuit path, which is sometimes necessary in the case of a short circuited failed battery

Good Luck.


YMMV,
MidCow3

Norcal001

This happed to me about a year ago, luckily my wife was at home when we experienced this issue. After some research I discovered when the vehicle is parked and off, but the lights remain on while doors are open the power is being delivered by the 12v battery. Also internal offline functions GPS, CPU’s etc.. the car makes so many noises while off, that power is being delivered by the 12v battery. Eventually it will deplete the 12v battery. On top of that we don’t drive the car that much so sitting idol adds to this issue.

solution:
I replaced factory battery with an interstate battery. In conjunction developed a trickle charge schedule every three months to maintain full charge. For convenience I wired in a trickle adapter cable.

hope this helps, works for me and provides peace of mind.

RandallC

Thanks all for your commend suggestions. Not exactly what I wanted to hear after spending a boatload of money on a luxury car. Hope a software upgrade eventually solves the issue.

a2023LC500

Happened to me yesterday.
I purchased a 2022 NX450h+ CPO with only 7,000 miles from Lexus of Reno.
Had it shipped here to my home in Everett, Wa.

I turned the switch to ACC to personalize some settings and in 10 minutes the entire power of the vehicle shut's down.
I didnt know what caused it as this normally dont happen on any car.
Did a youtube search and found the battery jumper points under the hood.
Hooked up battery charger under the hood, the car started making all kinds of interesting noises as each system gets energized again.
Charged the 12V battery fully, wife and I went for a 3 hour drive, it drove normal, then CEL came on.

Made an appointmet with my local Lexus dealer for Tuesday next week to check and clear the CEL fault and for them to check 12V battery.
I will share here what dealer say once I get my SUV back.

jsmith

I assume you can trickle charge using the underhood terminal? I want to fully charge the battery on my CPO before anything else although we do drive about an hour at least on a weekly basis. Also, on a longish vacation, I may want to put a trickle charger on it too.

OldManToad

I may be wrong about the 450h+ since I own the 350h, but it is my understanding that the 12 volt battery only gets charged when running the ICE. Therefore, when taking long trips, the ICE is running quite a bit and should keep the 12v adequately charged. That is also why when configuring settings on your car you should have it turned on in Ready mode and not in ACC mode. When the 12v gets low, the ICE will start and charge it back up. Also, during colder weather when heating steering wheel, seats, and cabin, or hot weather when running the AC, the ICE will run more frequently charging the 12v. I would think with the 450h+ that if you only make short trips in EV mode the 12v would lose charge. Does the 450h+ have a different DC converter that charges the 12 v from the traction battery?

Edison_Chen

I trickle charge from under the hood overnight using the CTEK MXS5.0 once every few weeks on 350h.

SgtLip

@RandallC Sorry to hear of your wife's and your troubles. I too have an NX 450H+. Mine is a 2023. I took mine to the Window Tint shop and that is when my troubles started the first time. We tried everything including a super duty charger and couldn't get it charge or jump start using the Pins under the hood. I was able to get the driver back door open and laid the seat backs down and climbed into the cargo area to raise the hatch in order to access the 12V battery. We had to let it charge for about 30 minutes before the car would fire up. It's done it one more time so I figured I needed to take action of some type to be prepared for the next go at it.

I already had the NOCO GBX45 Jump Box. But I figured that would just get me going again. I needed to do something with the battery since Lexus refuses to acknowledge there is an issue with their (now our) 12V system. I had already figured it out that it was from lack of use of the gas engine charging the battery. I started turning the EV off every couple of days to insure it would run and charge the 12V. I have also purchased the NOCO Genius 5 charger. It is a trickle/maintainer type charger. Every couple of weeks of not driving in HV mode or EV Only mode I put the charger on it overnight. I've not had any issues since performing this self service.

I just got the car serviced at the dealer for the 10K scheduled maintenance. I told them about the battery. They too checked it out and told me there was NOTHING wrong with my battery. I said of course not, I'm having to keep it on a battery maintainer to make sure it doesn't die again. But SOMETHING has to keep draining this POS battery. He said they couldn't find anything. I will say, it took them over 4 hours to do a 10K service so they had to be killing time doing something. And I sure hope it was investigating the system.

All that aside, I have already made my mind up that if it happens again, I will replace the 12V out of my pocket. But I can assure you it WILL be a better battery. I'm leaning towards the Yellow Optima Battery brand. They are designed for heavy electronic use.

But that's my story and what I've done and intend to do. Now you decide what path you will take. I hope it's easy.

Merry Christmas everyone.

lsft

For the 450h+, the DC to DC Converter will charge the 12V battery and while you are charging the car, it will also charge the 12V battery. However, the charging is low and slow.

sm20202

This just happened to me ('24 350h)

Weird behavior before the vehicle completely died
--Flashing "parking" warning light
--Wipers (very) slowly moving, out of the blue
--Lights fading

I COULD NOT TURN THE CAR OFF, yet it wasn't really turned on either - it was a mess; very frustrating and concerning if it happens when I'm not around.

Jumped battery after waiting overnight - car turned back on with some odd behavior (clock was set to a random time, nothing close to when the issue started).

More importantly, the check engine light is staying on (solid, not flashing) with constant reminder to visit dealership.

Has anyone dealt with something like this? I assume the battery needs to charge up a bit for the engine light to go off and hopefully nothing more serious. Would appreciate the group's experience/feedback!

NX450Guy

Yep, EXACT same thing happened to me at 90 miles. I was glad for the check engine light though because I thought that would help the service people zero in on the problem. Nope. They were clueless, just proclaimed my battery to be in perfect health and could not explain what happened or recommend any way to prevent it from happening again. Since I had it towed in, they cleared the check engine light. I mostly drive in EV mode on short hops and, thanks to forums like this, I discovered our 12 volt batteries lose their charge under these conditions. So now I switch to gas more often and will let it idol with gas in “ready” mode to make sure the 12 volt isn’t draining when I want to play with the computer or familiarize myself with the SUV with the air or heat on. So crazy how delicate this luxury car is. We shouldn’t have to stress this crap for the money we paid. Love the NX 450, but man, a dead battery is no joke at the wrong place at the wrong time. Never use ACC either. That will kill off the 12 volt before you even finish your favorite song on Car Play! I’m going to look into another battery that will do a better job than the one that came with the NX.

Also, know that if you leave the NX plugged in all night, that drains the 12-volt too. When the electricity is topped off but the cord is still plugged in, the computer stays on to “monitor” things and sucks up juice even when no actual electricity is transferring. It’s recommended that you unplug as soon as you stop charging to prevent the drain on the 12-volt.

Lexicon1

Am a new owner of a NX350h.
1) How do do you listen to the radio when parked without being in ACC mode?
2} How does one get into READY mode when sitting in car
3) Gonna have the car window tinted in the not so distant future, what do you instruct the installers that will have doors open for quite a bit of time?
Yes, I am new to the Smart button vehicle....
Any good videos on this topic. I saw a couple that were not helpful or were just confusing
Thanks
Looks like I now need another item to purchase and store in the cargo area besides an air pump, tire sealant and now an auxiliary battery jumper battery....what else does one need that Lexus did not provide?

Droid13

The radio will work in ON, ACC, and READY modes. With your foot OFF the brake, pressing the power button with cycle between OFF, ACC, and ON. Ready mode is of course attainable by having foot ON the brake. Only in READY mode will the battery not be run down so if planning to sit for a long time, READY is best but possibly at the cost of a bit of gas should the engine need to start to maintain battery levels. ACC mode should consume less battery power than ON, but note, ACC mode is only available if the feature is turned on within vehicle settings. If ACC Mode is turned off, pressing power button without using the brake just cycles between ON and OFF.

MrPrius

Been monitoring this forum for quite some time. It seems that the 12V battery are under sized for all the electronics the newer Hybrids need to support the vehicle. It also seems that the gauges and sensors all run off the 12V so if the 12V is out there is no way to have the vehicle transfer juice from the traction batttery, Maybe a design flaw?

Is there a way to force the traction battery to charge the 12V on the nx450h+ or RAV4 Prime (Both are from the same platform)

My 3rd-gen Prius doesn't have this issue unless I leave a light on inside the car.

my 2 cents

lsft

Let the car run in ready mode for 1 hour and let it turn off itself. That should help charge the 12V battery. In Hyundai PHEV, there is a button that allows the traction battery to charge the 12V. This is not a Toyota or Lexus only problem. If you google 12V battery issues with PHEV, BEVs, HEVs from most brands like Hyundai, Kia, Ford, etc....