The 12V battery in the RX350 is much different than the 12V battery in the RX350h. They would not be made in the same "batch". The auto stop/start system on the RX350 engine requires a special, much more robust and complex battery to restart the engine after each auto stop which is a much tougher duty cycle than on a hybrid. The RX350h engine is started by the traction battery, not the 12V battery. Sounds like typical BS from the service manager to deflect from the real problem and placate the customer. However, the lack of posts on this forum about RX350 12V battery failures is believable, objective data.

See the below video starting at the 8:20 mark for information about the "special" 12V battery in the RX350.

 

Thanks for posting, different battery, I found the video very informative and demystified the start stop system. Cheers.

 

Here is ome additional information on the charging algorithm issue. I was watching my Ancel battery monitor on my 2024 Rx350h this morning, I installed the monitor due to dead 12V battery issues for which the dealership replaced the battery. Prior to starting the car the battery was at 12.34 V range and around 60% capacity (and yes I've been driving a lot and daily). When I started the car, the ICE also started and the charge showed a 14.45 V output. After driving a few miles, the charge dropped to 12.85 V (capacity still low at 62% whie driving). I stopped in a parking lot and placed the car in park, still on/ready, When the ICE shut off, the traction battery increased to 14.45 V again, Sat for a while and when the ICE started it dropped back to 12.85 V, still a low 65% capacity/charge.

My conclusion (WAG) is that when initally starting the car, given a certain charge requirement, it will charge the 12V battery in the 14.45 V range, regardless of whether the ICE is running or only the traction battery alone is running. At some point, when 12V battery reaches a little higher charge and the ICE starts, it will drop the charge back to the 12.85 V range. However, when the ICE shuts off the traction battery increases the charge to the 14.45 V range again. One, I'm thinking the small hybrid 12V does not have enough capacity. Two, when the ICE starts up, the charging algorithm drops the charge down to the 12.85 range which may not charge the low capacity 12V well enough either.

When the ICE starts/runs, I believe the starter/alternator combo also charges the 12V? Or does it only charge the traction battery along with regenerative braking? For whatever reason, the algorithm drops the charge to 12.85 when the ICE is running and back to 14.45 when off. The ICE has to have some play in dropping the charge? All this may or may not make sense so let me know what you think, scratch your head, or have a good laugh, lol.

 

See attached for charging philosophy of our hybrids. Aux battery is charged by DC-DC converter using the high voltage hybrid battery, engine on/off status have no effect.

Under basic control the DC-DC converter varies the voltage to the aux battery, it may just maintain the battery or increase voltage to charge it. Under this regime of control is where I suspect the computer does not charge the aux battery long enough to cause dead batteries.

It seems in certain situations computer will revert to constant voltage control which will charge the battery, but from number of people with dead batteries it needs better algorithms…

Note the last paragraph vehicle preference is to supply lower voltage as to decrease power draw. This assumes 12v users are drawing constant amperage.

 

Got it, only the traction battery charges the auxillary. Perhaps one of the constant voltage critria is being triggered when the ICE starts under certain circumstances that lowers the charge? It seemed to switch to the lower charge when the ICE started and back to higher charge when off (and battery only 60% range). Understood that it has nothing to do directly with the ICE charging since it does not charge the auxillary. I'll do more tracking with my monitor to see if anything correlates with the switching from basic to constant controI. It happened when parked and running but I'll have watch my tachometer to see if it switches while driving. Very, very good information and makes sense. Perhaps they can modify the algorithm in the future without mileage suffering much. I'll study and digest this further and thank you very much!

 

Your voltage numbers are a little different from mine, but the patterns are the same. Your conclusions make sense.

 

this is an interesting thread. What really surprises me is that Toyota as been THE leader in hybrids for quite some time, so I'm really surprised they're running into a problem as this appears to be.

 

Yes I agree. It seems that if they used a better 12v battery a lot of issues would be eliminated. This coupled with a negative terminal under the hood that is closer to the positive and clearly marked.

 

Interesting issue today. Haven't had any battery issues since I started monitoring the battery, and installed the Ioniq trickle charger. Today, my Auto Detailer pulled it out of the garage, and I believe he left the key inside the cupholder as he was cleaning the inside and outside. 3hrs later, went to move it back in, car was dead as a door nail. Thankfully, using the Ioniq app, I just pressed the giant red button and gave it enough juice to essentially jumpstart the car. It's almost done charging now via my 220v charger. Battery life is showing 97% vs 0% when it was dead.

See below on the spikes. I can tell the neutral at the beginning was it sitting, first spike was starting it and moving it, the next big upward spike was after I jumped it and drove it into the garage. In between, it dropped like a leaf. Any thoughts on what would have killed the battery in such a short amount of time?

 

First off, congrats on the documented real-world, non-simulated demonstration of the Lexus Adult Diaper’s fully effective absorption effectiveness.

Did the detailer leave the car in ACC mode ? If not, then it almost certainly was the key fob communicating with the car while it was in the cup-holder, is my thinking

 

Covered by Wells

 

Looks like it was fairly low to start with. I always fully charge ours with a 12v charger when it gets at/below 12.4v, which is where sulfation starts to occur. When the doors are open, the vehicle draws about 8 amps which will kill the battery in several hours. I've not been able to measure current draw just from the fob near/in the vehicle, but I know the voltage drops pretty quickly whenever the fob is near the vehicle. .

If it was left in ACC mode, it would die pretty quickly as that pulls 25 amps or more, depending on if seat /steering wheel heaters and/or headlights are on.

Keep in mind that your battery is going to need to be fully charged with a 12v charger now. Just plugging it into the EVSE will not fully charge it. My 8 amp charger takes 4+ hours to charge it. Lower capacity chargers take longer.

This image shows a 12v charging cycle with the 12v charger at 8 amps. The battery had been at 12.5v the day before and suddenly dropped, shown in the next image. Not sure what caused the drop.

 

my battery is always hovering around that original mark in the image. Knock on wood, my wife usually drives the car everyday, especially with it being cold out right now, the engine runs longer than in the summer.

and I don’t have a real charger. Just the Ioniq trickle charger which is currently at 53% as I was using that to juice up the 12v. I could let that charge down to 25%.

 

I'd suggest leaving it on and in park(not plugged in)for an hour or so. That should get the battery up to a safe state. The 12v vehicle charging system will supply as many amps as the battery will take when in park. Sadly, driving it doesn't reliably charge it.

 

@WellsB , @GeneralKlinger - remind me where you guys pull the time/voltage plots from?
From the Lexus app or the Ionic app? Thanks.