Would getting a bigger/better 12v battery help? My guess is it wouldn't because it would be like getting a bigger gas cannister; eventually you're still gonna run out if it doesn't get topped up.

 

There is actually some folks who reported putting in an (Odyssey ?) AGM H6 in theirs in this very thread if you search, and it reduces/mitigates the problem - but does not eliminate it, as to be expected. The reason I thought it reduces the problem is that the AGMs have a lower internal resistance than the lead-acids, leading to their drawing higher charging currents and therefore faster/better "canister filling" over any given period of time, relatively speaking with respect to the lead-acid.

If I have to put in a new battery on my dime (post Lexus factory warranty), I'll put in a deep-cycle battery of some kind, perhaps such an Odyssey H6. To me, my priority in order of fixes is the (1) Lithium Hub or Ionic Emergency Start to recover easily from accidental battery deaths without any issues, (2) a H6 deep-cycle battery when I have to pay for it - to mitigate the problem to point where it does not matter to me in real-life (3) Leave the car on a battery maintainer at home if I'm gone for more than a couple weeks (4) If I have to give the car to a detailer, I externally pre-charge the 12 V battery externally, warn them about not draining the 12 V discharge while working on the car, then again charge the 12 battery externally after the work is done. That way, I have externally charged the battery less than 5 times over the last 1.5 years. I drive 100-150 miles every week, and above plan has worked for me in having NO battery coma/deaths at all in 1.5 years.

(Anyone is welcome to remove the sensor to be the guinea-pig, but please be sure to report back if anything happens in 1 - 2 years with the DC-DC converter!).

 

I've seen reports of the Prius and Rav4 hybrid also dropping voltage when in drive and picking back up in park and also of them having dead 12v batteries and premature end of life of the 12v battery. This appears to have started in the 2018 hybrids. I assumed they have the same charging algorithm as the Lexus hybrids. I did notice one report of a Rav4 Prime with the battery charging voltage at 12.8 to to 12.9 volt most of time, the same way my RX450h+ acts.

 

Yes, from Kelly's video, this entire converter-algorithm hardware-software certainly appears to be totally baked into the 4th Gen Toyota Hybrid system design - and therefore algorithm/hardware exactly same across the entire lineup across Toyota and Lexus. It would be interesting to watch what happens with 5th Gen Hybrid system, since the converter is even more integrated there, per Kelly in the 2nd video I had linked to above - so it would be even more complex to fix/replace any similar problems 12 V battery charging there by Toyota/Lexus.

 

I parked my 2025 450H+ at the airport for 15 days over Thanksgiving. It started right up. Average temperature over the time was 45 degrees. A friend has the 2025 500TX+. It also started after sitting in the garage for two weeks.

 

This is what I've referred to - some seem fine and others not. One would think if this was truly systemic all owners would be affected.

 

I think it's about how often the vehicle is driven, how long doors are left open, how long the headlights are set to stay on after shutdown, is ACC used, things like that, things a driver may not even think about or not know has any effect.

 

I've found that having the key fob stationary while washing my NXh made a big difference. I've killed my battery 4X. Have had a new one installed under warranty, but I think just taking the fob out of my pocket while doing things like washing the car made the difference for me. Haven't had any issues since doing that! I can tell by the message sent from the car after it sits for about 2 minutes after shut down. The message usually mentions the doors are unlocked. That to me signifies that the fob has stopped communicating with the car and all those systems related to that are off, which stops the battery drain.

 

The 12V battery died yesterday on our '23 with 16,500 miles. Luckily, it was in our 40F. garage. You Canadians are scoffing already, LOL.
We called Lexus Roadside Assistance to get a jump start, then drove to the dealer where they replaced the battery within 45 minutes. Prompt service!



Detailed story:

The flat battery could not be 'jumped' by our battery booster. The booster had been recharged a month ago, and we have used it several times to help others boosting flat batteries. But in this case, it wasn't strong enough to get the car going.


The dead battery symptom was a new one to me:

I went into the garage, then opened the rear hatch electrically to store some shopping bags in the cargo area. Opened the driver's door, got into the seat and pressed START, and several blinking dash indicators flashed on and off randomly. The headlights started blinking/flickering ONE SIDE AT A TIME too, really weird.

As an experienced Club Lexus member, I had the presence of mind to roll down the drivers window.
By then, I needed to use the manual door unlatch! The RX was dead as a door-nail...Proceeded to hook up our battery booster, no joy.


So I called the dealer who promptly dispatched a AAA emergency service flatbed. The attendant jumped it with his large, professional-grade booster. He said he had never jumped an RX before so I showed him the + jump point and the negative connection point on the other side of the engine bay. Told him why he should always protect the ECU on Lexus hybrids. He appreciated the advice.

SUCCESS! His booster provided enough power for the RX to start in the normal manner.

After that, I drove the 30-minute trip to the dealer, where we kept the 500h in the READY running state while I checked in. Of course, I rolled the driver's window down again, cause it was in the mid-20s F. <<---More derision from the Great White North

Told the service writer I would schedule other service after the holidays. Spent 10 minutes in the parking lot checking settings before setting off for home. Question in a separate topic.

 

What model of battery did they install for you? It happened to me for my 350h and got the 00544MFH50.

 

It should be a requirement that all road side service providers, contracted by Lexus, be trained on jump starting, and towing Lexus vehicles.

For our part, we owners should be well versed in jump starting the car and watching roadside service drivers like a hawk.

I also recommend that the OP, and everyone else, keep an electric powered battery charger in their garage.

Portable jump boxes are all well and good for an emergency on the road, but you can’t beat a real charger/booster to thoroughly recharge the battery. Sometimes, it’s just not convenient to wait for AAA.

By the way, those portable jobs work much better if you’keep them charged and recharge them after every use. (As the OP will undoubtedly do in the future.)

 

One of the positive features of the Ionic Emergency Start is that it is charged from the vehicle so it is always fully charged and available.

 

Oh, and to respond to @Lexus-SSA the battery that the dealer installed was the one pictured in previous posts. They obviously had one on hand, and didn't need to order it from anywhere else.

 

I have the RX 350 turbo, which uses the conventional alternator to recharge the 12v battery, and never have the dead battery problem even though I frequently leave the car in the garage for two weeks without moving the car or starting the engine. In addition, I have the NOCO boost charger as a back up, just in case. I am not sure if other turbo owners are as lucky as I have been (knock on wood); anyway, based on my quick review of the various posts on this forum, the turbo owners have not mentioned the dead battery problem.

 

And it blows my mind if someone is hesitant to use the Ionic Emergency Start, but not at all hesitant to remove the voltage sensor.