asj2024

Yeah, I am in several RX groups in FB and I have yet to hear anything about it there, so I don't think it's a widespread thing.

Nitrous

Add me to the list. Our battery died after a particularly cold spell. The dealer ‘tested’ the battery and said nothing wrong. We were advised to get a trickle charger because we don’t drive it enough. Apparently, not driving it for 2 weeks, we should expect the battery to go flat. Seriously, leaving the car at the airport for a 3 week vacation might leave us stranded.

my solution was to get a NOCO booster (GB70, actually) and have it charged up in the back of the car. The good news is I now know how to access the key slot for the car. (And they’ve replaced the drivers door handle with the ‘new’ handle that doesn’t freeze in cold weather - will wait for the next sub zero day to test it out-here’s hoping)

asj2024

I'd think two weeks is stretching it, isn't it? Not when the car has all these electronics running in the background.

Most things I've read say 2 weeks is at the border or beyond.

https://www.jdpower.com/cars/shoppin...out-driving-it
https://autoexhaustandtyres.co.uk/ne...ry-sit-unused/

Nitrous

I’ve never had a car go flat, after sitting at the airport for a week without being started.
i think it’s pretty clear that they spec’ed the battery based on the 4 cylinder engine ‘assumed demands’ for starting.
my wife told me at the last service appointment they tested the battery when it was cold. It failed and so, was replaced.

if the parasitic demands for these cars is that high, they need a decent sized battery, not just the minimum CCA to start this small engine.

Markfm

Just checking - is yours an "h" version RX, and it's the main engine compartment battery that was dead? (Edit - D'oh, the 12V in the back )

Curious as to whether this problem has been occurring with anyone who has a base RX 350 (2.4l Turbo), or is it something peculiar to the RX hybrids. (350h, 450h+, 500h)?

Urlik

It’s the 12 Volt lead acid battery under the floor in the back of the car. Hybrids put the 12 volt battery in the cubby the RX350 has in the rear under the floor. RX350s have it under the hood.

pcm888usa

Had the car for exactly 10 days. Parked in garage overnight unlocked. In the morning, the car was completely locked up. App and fob did nothing to wake up the car. Could not open the doors. Called Roadside and they were here within 30 minutes (impressive). Driver said mine is not the first one that had the problem. He was able to unlock the passenger door, popped the hood but did not find the battery. He got to the fuse book and used his booster to jump the car. It woke up and I had it flat bed back to the dealer. No sure what happened. Sighs.

wrinkle

I might have an interesting experiential data-point to add.

I just returned from a 26 days overseas trip, when I didn't have physical access to the car, which was left locked in my home garage. I fully expected to return from the trip, after a 20+ hour long flight, to have to deal with a dead 12 V battery, based on everything reported and discussed here - I'm convinced this is a marginal design problem by Lexus, fully validated by WellsB's excellent measurement data as above - and fully agree that it isn't something one should have to worry/think about in a premium "Lexus reliable" vehicle.

I had prepared by placing my jump starter and long cable (to reach the negative connect point of the engine block) in the front passenger area, so that I can access it easily after prying open the dead, manual door once I got back.

I had also found the excellent hack by WellsB great - to periodically remote start the car every 7 days using the App (I had charged the traction battery to 87 % before leaving) - so that it switches to "Ready Mode" that then charges the 12 V before it goes dead. The only problem was - I didn't realize that the car prevents remote starting if the inactive period exceeds 7 days. You can't do remote start if the car has been "off" for longer than 7 days - and I specifically tried this remote start hack at the 12 day interval, to space out the interval - and found out the hard way that I couldn't, as I had exceeded 7 days of inactivity before trying. Also, you can't do remote starts more than twice in succession, without physically opening/closing doors after that. So that hack doesn't work for longer than 14 days, to remotely charge the 12 V, in hindsight (without battery maintainer, which I find to be a chore, and trying to avoid unless I have to).

In any case, I got into the garage this morning - and to my utter surprise, found the car/battery alive ! It was able to unlock and switch to ready mode fine, which I left the car in for about half an hour, and even switched on the ICE during that for good measure - before driving out with the car. I wish I were able to gather the 12 V battery's voltage data at the point, but I was not prepared for that... (although prepared for the dead battery).

I think what saved the day was the fact that I was in waning NorCal winter, when the temperature isn't dropping too low, unlike in Canada or Northeast US - and maybe (just maybe) the 7 day inactivity puts the car into a deeper sleep mode with lesser 12 V drain (which, if a feature, would explain why one wouldn't be able remote-start after 7 days of inactivity). Whew!

In any case, at least one datapoint that was a positive surprise.

asj2024

So the 450h+ was ok after 26 days. I had left mine 5 days with no problems, but that beats the cake. So it's probably not a systemic problem affecting all vehicles or this would be all over the RX forums in FB. OR the problem only affects cars under certain conditions (I am in FL, where it has not been extremely cold).

Also good info on remote start having limit of 2x in succession, and with 7 day max limit.

I'm actually tempted to leave the car for a week and see what happens, just as an experiment. Turn off as much electronics as possible (eg manually turn off all the safety features that use sensors, though those should switch off automatically when car is shut down).

Maybe someone with a multimeter can do this:

https://www.alldata.com/diy-us/en/di...itic-draw-test

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.