I had looked at the Odyssey and found them claiming on their website that their current AGM's don't have any vent at all (completely sealed) - but would be good to have more information on that.

 

Our Jaguar had non-vented, trunk-mounted AGM batteries for both the main Group 48 battery and the little Auxiliary battery (which the factory installed on it's side, to increase trunk space).

 

From their install manual;

 

While the use of the AGM can be a no-brainer in very cold areas of the US and Canada - because they will mitigate frequent battery-coma situations such as the OP has noted without external charging -- for milder climate like California, the cost-effectiveness seems better in having the Ionic ES together with the plan to replace with new FLA batteries (that are safe for the cabin) every 3-4 years. Given the higher charging voltage requirement of the AGMs relative to the DC-DC converter's voltage at 14.2 V (max), AGMs will likely have a lifetime only as long as FLAs in our Lexi hybrids.

From their FAQ:

Do AGM batteries require special care?
Like any lead acid battery, keeping batteries at high states of charge continuously promotes maximum service life. It is best to prevent batteries from becoming deeply discharged, and stored in this condition for long periods, as this will cause sulfation of the oxide. It also may prevent normal recharging at a later date.

https://www.odysseybattery.com/news/...pl-agm-design/

 

Thanks for sharing WRINKLE & WELLSB. Consumer Reports just named the 2026 Hybrid NX its best small luxury SUV. While I agree they are well built, CR typically doesn't address issues like these in their reviews till years later. I've seen this glaring trend in other reviews (ex: Samsung icemakers) and no longer rely that much on them for purchasing advise.

 

CR had a 500H model's battery die on them while they were recording their video review of that car/model (the reviewer was babbling while in ACC mode) - you can search and find it on YT. They did show that fully happening in their video - and that it happened without warning. Its very common knowledge now - to CR and its viewers.

I read today from someone's post on Reddit that their Lexus dealer told that there is a "fix" coming from Lexus - but that's hearsay, and I'll only believe it when I see it, given how shameless Lexus and their dealers are.

 

Delete

 

Totally agree. My almost 3 year old battery wouldn't start during summer (70 deg day) while I had the rear hatch open and 1 door while vacuuming for about 10 minutes. It normally has only had a resting voltage before starting in low to mid 11's. When I did the Hybrid cable recall I had the dealer check the battery and they said it's fine.I don't think they did a true load test, probably just a conductance test. It died again on me while at a ski lodge. Temp was around 20 deg, car had not run for 2 days and after I loaded up to leave again no start. Both times I used my portable Schumacher. I brought it to the dealer and they replace the battery without argument this time. I installed an Ionic ES on this battery so now I should be set. Interestingly the service guy at deal told me they installed an AGM replacement battery and said they are seeing a lot of battery failures including their on the Lexus RZ electric vehicle. When I went home, I checked the battery while installing the Ionic and it was a standard lead acid battery like the original. (00544-MFH50). It amazes me how some service guys are so uninformed.

 

Just joined. First post, and of course, I'm complaining about my RX 350H that is 6 months old with 6K on it. Got in it two days ago and it wouldn't start. Then I couldn't get out of the car. Called the dealership to ask how to get out......now I know. Pull the door lever towards you twice to get out. Then I ask my wife....."What if I had one of my grandkids in a car seat in the back? How would I get the door open to get them out?" Other than the obvious method of breaking a window and reaching in right now I don't know.

The dealership had AAA come and jump start it. Then AAA left. I called the dealership back and said if you think I'm driving this car to you, think again! So, AAA came back and they towed it to the dealership. That was a Thursday.

Late Friday I got this VM from the tech guy:Hi Mr. XXXX, this is Greg calling from Lexus Service. It's about 10 minutes to 4 on Friday afternoon and I'm calling we got the vehicle into the shop, but we're not 100% certain what the problem is yet. The vehicle is actually on an electrical system test as we speak. As soon as I know more on it I'll give you a call right away. Um, but with the hour that we're at right now, it's probably going to be Monday before I know something concrete. So if there's any problems or questions, feel free to reach me at XXXXXXX If not, you expect to hear from me sometime on Monday. Hope you have a great weekend. Thank you bye-bye.

So, at least they are looking into it. I was initially ask if I drove the car at highway speeds during the week\month. And yes, I drive it at a very minimum, once a week at 60-75mph for the one hour trip to my daughters.

After researching this, it's obvious the 12V has discharged.

Now, one matter I complained about at the 5K service was the car, intermittently when going down a long hill, it will give a low vibration that can be felt through the steering wheel. In addition, when this occurs, the "Charge" indicator on the dash shows no charging is occurring. It will show no charging about 80% of the time during this vibration, and 20% it will show a charge is occurring. Of course, the dealer said they could not get this to occur when they drove it.

Needless to say, for a $75,000 car it's disappointing. I have a 2017 F-150 that has sat outside its entire life....after 8 years I just replaced the factory battery!!!

I traded in a 2020 Ford Explorer that was nickel\diming me to death. The car only had 45K on it. The sun roof mechanics actually broke on it. $850 to repair it. Then the low tire indicators went wonky. It's $125 per wheel to fix...and yes, it's the batteries in those indicators. And when one goes bad.....they all go bad. The grand finale was the tranny began doing funky shifts and non-engagements. Good by Explorer.

Hopefully they will find and fix what's wrong. There is no way I'm going to hook up a battery tender on a $75K car that get's driven daily. If this is the fix.....then it' will stay broken. If it stays broken, it will be gone.

 

It's in the manual, but Here's how to open your door if the battery is dead;

Once the driver's door is open, you can reach back and open the rear door to get the grandkids out.

The vibration you are feeling during long downhill runs is the engine spinning to provide engine braking. Once the traction battery is close to full or the battery cant accept more charge, the hybrid system switches to engine braking to maintain speed.

Sadly, dealers have a woeful lack of knowledge about the vehicles they sell. Driving on the highway has zero impact on 12v battery charging with a hybrid. The only time the 12v battery is reliably charged is when the vehicle is on and ready to drive "Ready Mode" and the vehicle is in Park. Most of the time when driving, the 12v battery is just kept from discharging.


The issue is that the 12v charging system doesn't provide charging voltage (>14v) most of the time. This affects all of the 5th generation Lexus RX hybrids and possibly the 5th gen RX350 as well. It also seems to be a widespread issue among current Toyota/Lexus vehicles. Basically, the system only provides greater than 14v while in park, 5 minutes after a remote start is initiated, and about once a month for about an hour. Most other times, its only providing 12.x volts which powers the 12v system, but doesn't charge the battery.

The available solutions(as I see them);

Disconnect the voltage sensor on the negative battery terminal. This puts the charging system in "fail-safe" mode and causes it to constantly provide >14 volts, like a traditional alternator system. This has an unknown effect on the vehicle systems and some have warned that this could cause the DC-DC converter to fail on your own dime. I also have concerns about constantly charging the battery, but traditional alternator systems have been doing that for decades and continue to do that today. It's the only thing that directly addresses the underlying issue, but could cause costly other issues.

Install a Bluetooth battery monitor. This does not address the underlying issue, but does give warning when the battery is dangerouslly low on charge. Charge the battery with a standalone charger every 2 weeks. This prevents the battery from dropping below 12.4v, which is where sulfation starts. Sulfation shortens the lifespan of a lead-acid battery. I believe this will prevent most dead batteries and premature battery failures. The timing can be tweaked using a Bluetooth battery monitor.

Carry a jump starter such as the Schumacher SL1648, which has leads that will reach the Lexus approved jump points. Familiarize yourself with manually unlocking the door and with jump startimg the vehicle. This won't solve the underlying issue, but will prevent you from having to call roadside assistance with the attendant inconvenience and delay.

Install a Ionic Emergency Start which is a Bluetooth enabled permanently mounted jump starter. This won't solve the underlying issue, but will prevent you from having to manually unlock the door and hook up a jump starter if the battery dies.

Personally, I use a Bluetooth battery monitor to indicate when I need to charge the 12v battery and have a Ionic Emergency Start installed, and also carry a Schumacher SL1648 to jump other vehicles when I encounter them.

 

WellsB. First, thanks for the dead battery, open door from the outside video, My issue is that I have MS and for me to attempt to twist around to unlock and open a back door from the inside is 99% impossible. The passenger door is doable.

As for after market monitors or carrying a battery jump start with me, I'd rather drive a '62 Falcon with no power steering\brakes or A\C. I didn't pay $75K to then put add on's because of poor engineering.

Now, I do have some knowledge of batteries. Both FLA's and Lithium. I have a golf cart that I repurposed 14 Nissan Leaf cells to use in it. The 48V system with a BMS works great. Before the lithium swap I had 8 6V Trojan FLA's so I do have a basic understanding of charging volts required to bring a pack to full charge. But...that's small stuff.

Now, if you could, expand a bit on the information you posted:

The vibration you are feeling during long downhill runs is the engine spinning to provide engine braking. Once the traction battery is close to full or the battery cant accept more charge, the hybrid system switches to engine braking to maintain speed.

Ok. That may make sense...however, the dealer tech's have never stated this. Besides, if it's suppose to vibrate and make the noise that it does, again, poor engineering. I can't believe someone at Toyota said....."Yeah....that vibration is just fine".

Sadly, dealers have a woeful lack of knowledge about the vehicles they sell. Driving on the highway has zero impact on 12v battery charging with a hybrid. The only time the 12v battery is reliably charged is when the vehicle is on and ready to drive "Ready Mode" and the vehicle is in Park. Most of the time when driving, the 12v battery is just kept from discharging.

This statement doesn't make sense to me. If the 12V only charges when the car is in the READY mode, then where is it receiving the charge from? The engine isn't running to turn (what I assume to be) the alternator. So how's that work?

In addition, when driving if the 12V battery is just "kept from discharging" how can that be? A fully charged 12V FLA is at 12.8V. And the same 12V FLA needs a charge when it drops to 12.2V. So if the system is "kept from discharging" is must be getting charged from the alternator. And it doesn't make sense that it would hold the charge to say 12.3V when it could simply provide it a full charge up to 12.8V.

The issue is that the 12v charging system doesn't provide charging voltage (>14v) most of the time. This affects all of the 5th generation Lexus RX hybrids and possibly the 5th gen RX350 as well. It also seems to be a widespread issue among current Toyota/Lexus vehicles. Basically, the system only provides greater than 14v while in park, 5 minutes after a remote start is initiated, and about once a month for about an hour. Most other times, it's only providing 12.x volts which powers the 12v system, but doesn't charge the battery.

Again, how can it charge when it's not running an alternator and why would charging be limited to when the vehicle is only "remote started". Whose bad idea was that? It doesn't make sense to me that this is how it works.

 

Using engine braking to maintain consistent driving characteristics is good engineering to me. Vibration and noise is an unwelcome side-effect, but preferable to a sudden change in driving characteristics; sudden unexpected acceleration in this case. Lack of knowledge in dealer techs has been firmly established. I've known more about the vehicles I drive than 99% of mechanics, for my entire driving life, over 40 years.


There is no alternator. There is an onboard 12v power supply / charger. It is powered from the traction battery when the vehicle is in the ready to drive state. I believe it operates at 12.x volts most of the time for fuel economy reasons, but that is conjecture. It is certainly poor engineering practice from a lead-acid battery point of view.

Based on your position in regards to charging the battery periodically and/or using a jump-starter, it looks like your only choices are to keep experiencing dead batteries, get rid of the vehicle, or disconnect the 12v battery voltage sensor, with its attendant unknown risks.

 

Needing to charge a battery on a $75,000 car with 6K miles just so I can use it seems more than odd. If this is the recommendation, then this first Toyota brand for me will be the last. I'm a 70YO man with MS. I don't have time to screw with a brand new car. I'm fortunate enough to have time to keep my body in shape to do things.

I know I can hop into my 9 YO F-150 and it will start right up and take me anywhere. I also have a 2000 Mustang 6cyl convertible with 45K. I can do the same with that car. If I wanted to plug in a car, I'd have bough a plug in model.

I doubt Honda has these issues with their hybrids, but I could be wrong on that.

But believe me when I say that if this keeps up, it won't stay under my ownership for long.

Interestingly enough, a Google AI says this about the Lexus 12V battery:

• Automatic Charging: The system automatically manages 12V battery health, utilizing the high-voltage system to power electronics and keep the 12V battery topped off.

 

Google AI recently gave me incorrect information about the tire pressure for my motorcycle. I reported that the information was wrong, and gave it the correct information, giving the owner's manual as reference. The next time I looked, the AI answer was even further from the correct values.

It's flat-worthless to me.

 

Well, you're not saying if the AI answer in this specific case is right or wrong. And that's a pretty important piece of information.

In some further research it appears that the 2025 RX 350 H has a diagnostic screen that can be accessed from the car's touch screen. It's been referred to as the "Hidden DX Menu" but appears it's not all that hidden when it's all over the internet.

However, apparently (and I say apparently as I don't have my car to double check this) it will show the 12V battery voltage when accessing the menu. This video , when accessing the "Vehicle Single Check Mode" shows the voltage of the 12V battery. In the video it shows the battery voltage at 10.4V (less that an "at rest" full V of 12.6-12.8V. A dip below 9.6V on a 12V battery under any load would indicate the battery is no longer any good.

So, if this video covers my 2025 model, I should not need any aftermarket product to check the voltage (and health) of the car's 12V battery. The video also has shown the 12V battery is receiving a charge when the vehicle is running. The video states "alternator is running". I would think that since most people understand what an alternator does, that makes sense.....even if that car doesn't have an actual alternator.

In any event, I'll wait until the tech guys at the dealership tell me what they have figured out.

This car had (and maybe will continue) to move up the list of the most favorite car I've ever owned. I've bought nothing but new cars my entire life (well.....don't count those Chevy's and Fords that I paid $200 for when I was in college). This Lexus is simply a very nice vehicle to drive.