DEL92

Is there a circuit breaker that protects the 12v system from the 'Jump Pad' located in the fuse box ?
I'm trying to wrap my head around why the vehicle remained disabled after the road service technician connected their jumper cables to the Jump Pad.

Recently experienced a discharged 12 v battery following a 45 minute drive on the freeway to a nearby event. Lexus Roadside assistance was very responsive and arranged for the dispatch of a local service provider to address the 'dead battery' situation.
The service technician was apparently not too familiar with Lexus RX350h models. The technician accessed the jump pad located at the fuse box for attaching the positive cable. They seemed to be at a loss where to land the negative cable. They tried landing their negative cable at several different places on the engine in close proximity to the fuse block. The first few times they landed their negative cable, there was a sizable spark and the circuit breaker protecting the service vehicle's power tripped open requiring the technician to reset it. On the third time, the circuit breaker remained closed when the jumper cables were landed, but it appeared there was no power getting to the 12v system and the vehicle could not be started. I requested the technician use his voltage meter to check we had 12v at the Jump Pad. He verified we had voltage at the pad. In the end I had to have the vehicle towed to my local Lexus dealer for repairs. They reported needing to replace the battery (under warranty) but had no explanation why the 12v distribution supply couldn't be recovered when the voltage was present at the Jump Pad.

I agree with everyone who is about to respond "the negative cable goes to the bracket to the right of the engine." From reading the Owners Manual I understand the bracket to the right side is the intended landing point for the negative cable. It's to bad the road service technician wasn't more familiar with this point.

Any feedback or comment if the 12v system has a circuit breaker between it and the Jump Pad.

Thank you for your time and considerations,
DEL92

StefanoS

My 12v battery was dead today, after I had returned from a four day trip to Palm Springs. We took our gas hungry Sequoia on this trip, as we towed our travel trailer for this brief getaway. I moved the RX when we returned on Friday. Today when I approached the car, the door would not open. I used the mechanical key in the fob and as expected, nothing happened when I hit the start button. I opened the hood and connected my NOCO Boost XL GB50 to the point in the fuse box and the ground. The engine started right up. I have never used anything other than "READY" mode in either of my two 450h+ cars. I had already pre-wired a battery charging harness to the 12v, as I have read of problems that others have had. I had previously charged the 12v on two occasions, using my NOCO Genius 5 charger, in an attempt to keep the 12v battery up to snuff. All of my trips in town have been in EV mode and longer trips in HV mode. Needless to say, I was a bit surprised to see this occur, as I've been fairly religious, since my purchase of this car last October, in trying to maintain the 12v unit in a good state. I don't have any other items wired to the electrical system that might be causing a parasitic draw on the battery. The 12v in these cars is a very small unit and I am wondering whether it should be replaced with something a bit beefier. Others have had their Lexus dealer install a larger CCA battery, under warranty and this may be the way to go.

asj2024

I'd be interested in knowing the cause of the 12V failures.

I've owned a Prius for 15 years now and not one single time has it ever gotten a discharged 12V battery...except when we forgot to turn off a light.

I use Dr. Prius to check the voltage of the battery, so maybe I'll start monitoring it daily to see whether something is draining the thing. I mean, we do know the car has sensors all over (just going close to the car with the fob switches on the handle lights). It also is connected to the net, even while not started.

ps. We sometimes go on week-long or more trips (e.g. cruise or travel abroad). If this happens, it's good to know I can start the car remotely to charge the 12 V (at least until 2027, when I need to pay for it)

MooneyPilot

Add my SO to the list of “dead battery syndrome” sufferers. After 5 days of non-use in our garage, she found the battery so dead that we shoulda dug a hole and buried it. When I returned from work, I put the booster charger to work and got the rear hatch to open. Found the battery and my meter showed 3.9 volts😱😱. Serious WTF moment. Attached my SO’s 45+ year old dumb charger directly to the battery for a good 5 hours. Once the 9a output dropped to less than 2a, I removed the charger and plugged the level 2 for the night. Next day the battery was 12.3 and within 2 days of non-use it was 11.8 Scheduled for service to check it out as the car is going in to body shop for 7-10 day repair. I gotta bad feeling that this battery won’t survive the body shop stay and some minimum wage worker is gonna jump start it and crispy critter something expensive.

RBach

Adding another data point to this thread.
Brand new 2024 RX 450h + essentially dead on (delivery) arrival. Had to jump start the vehicle twice in first week of ownership.
Have checked daily for anything "on". Haven't found anything yet. Have tried keeping the vehicle both "locked" and "unlocked" overnight; no difference.

Local Lexus dealer (excellent team) tested the system, suspected just a dud battery, replaced w/ a deep-discharging version of the 12V. They tested for parasitic draws for two hours prior to replacing 12v battery; nothing showed up.
Said let's try the 'replace battery' route for now, and watch.

Still have a voltage drain however. This new battery is being depleted each night. Down from "new battery" charge to 11.76v at this point, and dropping daily.

Anyone have recent Lexus experience servicing parasitic draws, and likely device/ circuit candidates ?

Sad to think such an expensive vehicle needs two plug-ins daily: one for the hybrid PHEV battery system, and one - to trickle charge the 12v ? Back to the Future, eh ?

alextv

What did they say the ma parasitic draw was? A full charged battery after 20 minute rest should read 12.7v. How many nights to attain that 11.76v reading? What kind of driving each day? Are both keys far away from car at night and try disable the digital key in Lexus app as in background may try to communicate continuously. Now my experience with my 2020 ES300h UL. Software updates fixed a lot of draw but still acts just like yours. Most people will not test battery voltage so don't really see the drainage each day. My car driving around 15 miles per day will see battery depleted more each morning down to as low as 11.76v but will still go in ready mode. Drive it and goes back to 12.2 after rest. Even long trips the charging system will never fully charge the battery like an alternator does probably to preserve the HV battery as that is what charges the Aux battery. Once /mth I put a trickle charger on to fully charge the battery but the way this system is designed probably don't have to. No one I have talked to fully understands the aux charging systems in the hybrid just it charges from the HV battery. So long as the parasitic draw is not too high and will give a 2 week ready mode it should be ok but that is also from a fully charged battery and not starting the 2 week point at 12.1v. There should be a switch to completely cut off the DCM module that is causing this excessive drain. A test here for you is to fully charge your battery and test voltage each morning.

Julius071

Damn that a huge voltage drop! Sadly, I am preparing for the dead battery situation in my 23 RX 500h. Currently researching to change out OEM battery for a Odyssey Battery with wife approval pending. for me, why bother when we can change out oem battery under warranty at the dealership?!

alextv

Lexus requires a full diagnosis of battery before warranty replacement. Majority of situations they will charge and test as good. Onboard charging of Aux battery at least for my ESh never brings battery to 100% as alternators do. Mine after 3 hr trip waiting 10 min is around 12.46v which is 80% by chart. Charging is done by HV battery and am sure Lexus has refined all this to work eficently.

DEL92

So what am I missing, we bought Lexus vehicles, not market-entry-level products ?

Please don't misunderstand me, my wife enjoys the comfort and amenities of our RX350h very much. At least 2-3 time a week I have people asking me about the RX line and how I like the vehicle.
But should it be put upon the vehicle owner to keep some or any of the following items on hand because the battery dies or becomes discharged too low to start.the vehicle:
- Portable battery jump starter,
- Battery changer or trickle charger,
- Battery charger harness installation,

I didn't see any of these items listed as add-on options for the vehicle.

Thanks in Advance,
DEL92
RX350h Premium Plus / Eminent White Pearl

alextv

Afraid this is what we are all facing now. It's not just all the computers with the parasitic drain as in past but the DCM module seems to be what is causing a lot of the problems with constant communication. Software updates have been and continue to minimize this problem. Probably a good idea to at least keep jumper cables in car as it only needs a 12v source to go into ready mode then 14.2 volts available to charge battery.

asj2024

If it's the DCM then I was right in that it's the connection to the network that is causing the drain.

First thing I would do is opt out of Drive Pulse, as the thing might still be running even when you stop the car and is constantly sending out updates on itself and its location.

But still lotsa connections to the outside in this car.

If you go in the app to INFO --> SUBSCRIPTIONS, you can see all your subscriptions (trials at the beginning). You can cancel them it seems, though I would not do that until sure this is what's causing it. They're all pretty cool and useful.

alextv

Agree...I did notice when my subscriptions ran out the battery does not drain as quickly but you want to keep them if in your trial so just have to deal with the battery issue. Like I said most people don't check there aux voltage at all so don't realize the problem. Also when checking don't use an app connected to obd as that reports what computer sees at a point. Measure at jump port or battery. I do probably once /mth put on battery tender and it charges fully overnight. Also want to point out that I generally don't see the voltage below 12 anymore.

wrinkle

I posted about my surprise 26 day battery survival on the 450h+ - but I will also note that I had switched off the App's Drive Pulse (primarily to avoid sending potentially misuse-able data to the wild, unrelated to battery drain) during this period.

asj2024

Thanks, great data point.

Yeah, that does support the potential of Drive Pulse (and perhaps other connected services on the car) to help drain the 12V battery.

So besides preventing misuse of your private data, turning this off can also help keep the 12V healthy

wrinkle

I strongly suspect there are multiple factors at play (I used to get paid to do reliable system design , so speaking based on that experience)...

One is there is definitely defective batteries in brand new cars - such as in the experience by RBach below. And in my car, there wasn't evidently a defective battery. This is a problem that only Lexus/user can fix, by replacing the battery for those that have it. From Stefanos' experience, I suspect even he might have a defective one. Also "defective"/non-defective isn't exactly a binary categorization here, since we are talking about an analog signal coming of the battery (voltage) that leads to the problem. WellB's measurements showing the degradation, BUT him never actually having a dead battery, proves this point.

The other is parasitic drain, which is something we/users can try to mitigate - assuming the defective, shipping battery is not present in the car. While I'll not claim that stopping the Drive Pulse made a difference in my case, the not-so-cold temperature (say, relative to Canada or Northeast US) did surely make a difference, from the perspective of battery physics.

Another detail: When I had tried and failed to remote start after 12 days, I had also tried "Refreshing" the "Status" screen in the App - the "Tire Pressure" and The "Vehicle Information" one-line status dates didn't update from the day I had stopped using the car to begin with (the beginning of the 26 day period). In other words, this probably suggests it got into a deep-sleep state and did not transmit data in that state to the Lexus servers - probably reducing the parasitic drain. In normal usage, that status updates fine. Also, I don't have any after-market devices attached to the car.

I'll also add that the previous ICE car I owned (an Audi from 2014), I used to have a 4 mile commute to my work in that car for the most part - very short hops. The battery had died and had to be replaced by the dealer in 2-3 years for that too. So usage model of the battery definitely matters, as does temperature etc. - despite being a pure ICE and not having parasitic drains like a heavily computerized cars as the modern ones.