WellsB

The battery and 12 volt systems in the vehicle are charged/powered by a DC/DC converter that draws from the traction battery. It doesn't matter what driving mode the vehicle is in, EV, HV, Auto EV/HV, or Charge mode. It always charges the same.

As best I can tell from watching the battery monitor app, it charges the battery any time the vehicle is park and in Ready mode. By "charging," I mean the voltage goes over 14v.

After putting it in drive, it may charge for a few minutes, but then drops voltage to the point where it is powering the vehicle, but not charging the battery. Occasionally, I'm guessing once a month, the charging system will actually charge the battery while driving. It seems to be all time based and not voltage based.

The only other time the system charges the battery is about 5 minutes after remote start and for the next 15 minutes, until the remote start times out.

I put the vehicle in park any time I am stopped for more than a minute or so, and use Remote Start religiously when on road trips. This has resulted in the battery keeping a higher state of charge, though still not fully charging. At home, I use an external charger as needed to keep the battery above 12.4 volts resting

LeX2K

People are using these cars in a way that is intuitive which causes the battery to go dead. IMO it's that simple.

tammap

A simple device like this can tell you everything you need to know at anytime and in any situation of your low voltage system!

jctscz

LEXUS NEEEDS TO SIMPLY MAKE THE LITHIUM BATTERY PART OF THE CIRCUTRY TO MAINTAIN THE 12V SYSTEM - THE PASSIVE CHARGE CONCEPT IS NOT EFFECTIVE FOR ANY LONG TERM SHORT RUN OPERATION AND USEAGE.

THE ONLY REASON THEY DIDN'T DO THAT WAS SO THE FULL HP WOULD BE AVAILABLE ON DEMAND AFTER THE ALL ELECTRIC OPERATION FULLY USED THE BATTERY ELEMENT ALLOCATED TO FULL ELECTRIC OPERATON (ie In consistent short distance operation as full electric car - which I did until the battery failed - now I have a 12v separate charge method.--HOPEFULLY LEXUS MAKES THE SOFTWAR MODIFICATION NECESSARY TO HAVE THE LITHIUM BATTERY ALSO COMMITTED TO MAINTAIN ADEQUATE CHARGE IN THE 12V SYSTEM.

THEIR CORPORATE PROBLEM IS THE MARKETED THE 360 HP ... BUT THAT IS ONLY AVAILABLE WITH THE 4 WHEEL ELECTRIC BOOST - WHICH IT IS MY ASSUMPTION STOPPED THEM FROM RISKING IT'S UNAVAILABIITY BECAUSE OF THE USE OF THE THE LITHIUM BATTERY TO SERVE ANY OTHER FUNCTION (like keeping the 12v system fully charged)

DEL92

WellsB, I appreciate your detailed explanation of when/how the 12v battery is being charged, Don't think I have seen anyone else having the data to break it down like this. Seven months after I picked up my 350h, I - like others - have experienced a dead 12v battery situation. I had driven about 45 minutes on the freeway then parked the vehicle, two hours later I couldn't get in to start the car. Using the key the Tow Service driver got the door open and the hood up but couldn't get the 12v system to power up using the jumper pads. Every time they landed their Pos cable to the pad, the circuit breaker in their truck tripped. Had to drag the vehicle out of the parking stall with all four wheels in full-lock and haul it to the dealership.
Like others have commented, I hope Lexus re-engineers the DC-DC Charger algorithm, and rolls out a service recall & update.

DEL92

tammap. That is a great idea.
Here is a link to one (available through Amazon) that is CE, FCC, RoHS Certified.

Lexus-SSA

Hello all,
I have been watching this discussion for while. I am a computer engineer myself. I appreciate all the technical and measured explanation of the status of the battery, but it puzzles me that me and a friend bought our 2023 350h Premium 14 months ago and I have driven the car in all sorts of way (Short distance, long distance, parked for 4 days in garage, driven 900 miles in a day, parked on my driveway for 3 hours while waxing in off mode but the doors unlocked.) and so far the battery has been good. Neither of our cars have had any battery issues. I am wondering if some batteries installed by Lexus are defective in nature. Our cars were made in Canada in May 2023. I also have another friend who has the 2024 NX plug-in hybrid and zero battery issues. So puzzling!!!!

wrinkle

Technically speaking, some batteries may indeed be defective, but its highly unlikely that such is true for majority of cases. This is because the fundamental problem isn't with the battery per se, how its health is maintained (or not, in Lexus' case) by the charging algorithm. Batteries, like many other electronic components, aren't binary good or bad - their health lies on a spectrum. Where a particular battery is on its health spectrum depends strongly on how its used/maintained/charged. In this particular problem case, since the charging algorithm is deficient (i.e. does not charge the battery adequately when the car is in motion - see my post number 70 for hard data, in this 652 post thread if you'd like, among other posts), so batteries get discharged and degraded to various extents during the use of the car. I copied/pasted the same image below. Ignore the noise around the voltage values - that's due the A/D conversions, since this data is pulled from the Engine Control Module off the OBDII port, not directly from the 12 V battery.

On one hand, if someone is often parking the car and sitting in it often, the battery gets charged. However, if someone is simply driving the car around in "D" gear, without in "P" gear/state much, the battery doesn't get charged adequately or often enough. So you can see how someone's driving style ends up affecting the charging of the 12 V battery - all because the charging algorithm is flawed. If that were correctly designed, the 12 V battery would get charged all the time, especially when the car is driven. Ideally, you'd want this happen in a feed-back loop, such that if the 12 V battery drops below a threshold, the car should immediately start charging it automatically - obviously that isn't even in the design of the Battery Management System.

This is particularly a problem for the 450H+ models, both NX and RX, because these have higher drain due to all the maxed out features and frills. 350H and 500H can be optioned with or without many power-hungry frills/electronics, but Lexus/dealers sell the 450H+ only with maxed out features and are those are therefore at highest risk of battery drains/deaths.

The fix is in the battery charging algorithm, which should be doable with a firmware/software update, if only Lexus were to do it. If they simply test the car at the dealer in the Parked "P" state, they will not even figure out the problem, since the lack of charging only happens in the "D" or driven state of the car.


20 Minute Drive to the Store - Battery Only charges when in Parked State, and very little otherwise

LeX2K

That most definitely looks like a software problem to me.

Markfm

I ended up picking up a Bluetooth battery monitor, ANCEL BM300 Pro Battery Monitor. I went the AliExpress route, $25, got it in 10 days; it's also available on Amazon for $43.

Voltage reported matches what I see with my handheld meters, and installation was trivial. It only draws 1mA itself.

wrinkle

The stock/factory battery is not a run-of-the mill Flooded Lead Acid, as far as I can tell. I decided not to monitor (or trust) voltage vs state-of-charge of run-of-the-mill lead-acids as found in standard tables, and instead monitor how much charge (A-h) is being pumped to fill this Panasonic battery when I occasionally use the external charger. Today, for example, only 1.5 hours was necessary to fill it with my 5 Amp charger - implying it was already charged at (60 - 1.5*5)/60 = 87.5 % charge during my normal use of the car (where I don't keep it deliberately in parked state, etc - to charge the 12 V). I will be most curious what happens in winter. I haven't had any battery deaths since happening on 2 days in early April (when temperature dropped suddenly to 4 C minimum in California).

It seems like Lexus has reduced communication with the servers by the car, reducing the problem (?). However, staying in ACC mode or keeping keyfob outside of a Faraday pouch within 10 feet of the car will still be risky, I think.

DEL92

Wrinkle, this is eye-opening data !
A 12v vrla battery needs to be kept at float voltage level to maintain a charged battery.
Most every VRLA manufacture specifies float voltage should be 2.25vpc (13.5v).
Most VRLA manufactures specify charge voltage should be 2.35vpc (14.1v) for 6-12 hours depending on the battery discharge rate.
If the data you have collected is consistent with the other RX vehicles experiencing battery issues, I would think Lexus engineers would want to be entertaining some design review of the software managing the dc-dc charger for the battery as the data presented clearly indicates the battery is not being maintained at battery manufactures specified float voltage.
That said, there may be some extenuating circumstances we are not aware of. The 12v battery is contained in the rear boot (spare tire well). Ventilation in the well is not the same as the ventilation available under the bonnett (front hood). Battery manufactures also have temperature compensation specifications for the float and charge parameters. If the ambient temperature is 95°F or higher, temperature compensation for charging voltage is necessary. That compensation is typically -5m V/°C Cell.

What did you use to log the battery voltage data. As a Uninterruptible Power System engineer (for 35 years), I'd like to replicate the testing you show.
Thank you DEL92

P.S. apologies for the 'english' auto references, too many years owning my 1973 Triumph TR6, and working on other's Spitfires, TR4s and TR6s,
My main ride is a Lexus RX350h Premium-Plus Eminent White w/Macadamia

wrinkle

The data was collected with Bluedriver, on the ODBII port. It has a module that supports the Lexus/Toyota voltage data from the ECM. There are several others in the thread who have measured the voltage directly from the 12 V battery terminal using the monitors that Markfm and others have linked to.