Well, I've been bit. I don't use the vehicle in ACC mode. I drove it in the morning to the gym and got home without issue. A couple hours later I tried to go to Costco and the RX was dead as a doornail. Couldn't unlock it. Had to use the mechanical key to get in. Learned the hard way that there is no mechanical backup to get into the hatch where the battery is. I had a jump start box (that I bought because of all the issues people reported with RX) but I had it stored with the spare tire near the battery. That's a mistake. I couldn't get back to it. I called Lexus Roadside Assistance and they sent a tow truck. Tow truck driver told me they see a LOT of Lexus service calls, these days. He connected his jump box under the hood and commented that my 12V battery was registering only 6V and 0% health. Awesome. Tried to jump start but no success. Lots of flashing warning lights and even the head/tail lights were flashing erratically. Ended up having to get towed to the dealer. They said they'll get around to looking at it sometime in the next week. In the mean time they've put me in a base-trim NX250.

Side note on the NX. Physically, it's noticeably smaller than the RX (expected) but I could see how that may fit some peoples needs better. The 250 engine, however, is a noisy dog and Lexus should stop using it. Truly awful powertrain. I don't think the RX handles particularly well, but the NX is noticeably worse. The small infotainment screen is sad. And no heated steering wheel is unpleasant in this weather. Also, every time I drive a vehicle without a 360-degree birds-eye camera view I am reminded how much that is a "must-have" feature.

I hope Lexus replaces my battery without argument. I don't want them to just try charging it and sending me on my way. It's also ridiculous that these vehicles seem to both have improper battery management systems and ZERO warning.

 

@CommodoreAmiga Maybe people should periodically load test their batteries?

 

This is so frustrating already. The parasitic drain is just random. I reported this to the dealer while on 1 year service. I showed them screenshots of the battery levels (from the tester that I installed). They kept the car for couple days to monitor but found no problem. They keep on asking me if I had the remote key near the car. I don't really care if it is ... it still should not have this problem and if they know it is what is causing it then they should fix it!!

In addition to having backup and monitoring gadgets, I suggest educating anyone who uses your car about the mechanical keys/locks. While I was on overseas holiday for a month, my son took the car out of the garage one day as he needed the space. It would no longer start when he was going to put the car back. The problem is, he locked himself in. He's not familiar with car, did not know about the mechanical door latch. Fortunately, he was able to call me just before boarding a plane.

I also recall from one of the lengthy threads that an owner's wife locked herself in the car.

FYI. I had this problem before I went overseas and so started the car remotely every now and then thinking that it will charge the battery. Obviously, that did not work! I bought trickle charger and tester.

 

I guess I'm going to have to. This isn't something a modern vehicle should need, though.

 

Great information on this thread. Thank you all. My take aways are to not use the ACC mode, and minimize the times of the automatic shutdown of the lights.

 

I agree. It seems as though the battery is undersized for how people use the car, And a bunch of bad ones. I know in my boat (heat, pounding of waves, etc.) the batteries don;t last as log as car ones, but I once had a Corolla that had the original OEM Toyota battery for over ten years.

 

Judging by the number of complaints here, the 12V battery is way undersized. Do better, Lexus.

 

Thanks for sharing, immediately got two of them after seeing your post yesterday! We have both a NX and a RX that is garaged and each gets driven at least once a week. Being slightly paranoid from all the stories especially during colder weather, each of the 12v get topped off once a week through a trickle charger. Had the same situation where the NX about a year ago didn't start during the colder months, and since then had to buy a portable jump starter for travel, and a tricker charger at home. It's annoying for sure, but I've gotten so used to the process that it's not bad. Very different story if the vehicles were not garaged though and it would drive me nuts. The trickle charger we have basically shows the voltage and battery 'capacity percentage' upon connecting, and it always seems the NX seems to be lower than the RX. Probably since the NX is using the digital key, and the RX I removed it for about a month to see any differences. I'm weirdly more confident in the RX though since it's newer. Bought two of those Ancel BM300 bluetooth battery monitors to stick in back of each since that was more convenient, and Amazon was running a sale. Will see how those 12v do if we make it more than two weeks without driving.

 

Hopefully this is the last time but this lemon is really starting to drive me nuts. I have a 2023 RX350h that I bought in March 2024. I had three instances within two months of my battery dying and I had to call the dealer to come help. I educated myself on how to fix the problem each time. For the last six months, when it dies, I can use my jump pack to start it. I am one of those that drive less than 5000 miles a year so I assume thats part of the issue. Two weeks ago I wanted to go see my daughter which is a 100 mile drive. Car had been sitting for at least ten days. Worked perfectly. Three days later its dead. I used my jump pack and it started just fine. I went out last night to test using the fob to remote start and it failed. Couldn't get into the car without the normal process to get into a dead, locked car. I tried to jump it again but this time it would not take. My jump pack

Schumacher Electric Lithium Jump Starter and Portable Power Pack SL1648

has the process to do a deeper jump, which I did. It started the alarm horn blaring, scared the living poopoo out of me and my family. I removed the pack and it slowly died down but the car continued to flash lights and made a weird, constant clicking noise. I left it and went to bed.

I had accepted that this, my third Lexus, was no longer the brand I wanted but I had a process to get me running. But now that process fails. I can't let my family drive this car anymore until something is done. I called Lexus service an hour ago and someone is on the way so we will see how it goes. I told him he better bring a battery as I feel mine is really just junk at this point. Trying to keep my cool but this car is really testing me.

Lexus just came and took the car. I guess their jump pack is must more robust than mine.

My wife just made another comment. We typically hand down our cars to our kids. We could never hand this down to my daughter. If she got locked in or her baby got locked in this car, there would be hell to pay. So this car is mine until I die, I guess. Lexus, I am incredibly disappointed in you now. I really want my 60K back please.

 

I do periodically load test my batteries. The battery in our RX450h+, which is a bit over a year old, has almost no loss of capacity.

The biggest issues are the random increased parasitic loads and a charging algorithm that only keeps the battery half-charged.

If i didn't monitor the battery voltage and periodically charge it, i know i'd have suffered more dead batteries and loss of capacity due to sulfation.

 

The 12V battery in the above picture looks small for a car loaded with electronics like the RX350h. I notice that the label reads "20HR 60Ah CCA 345A". Not sure what 20HR indicates, but in comparison, my previously owned 2013 Avalon Hybrid had a much physically larger Panasonic S65D26R battery that had 75Ah and 750CCA. I realize CCA is not important for a hybrid, but Ah (Amp-hours) is. The Panasonic Avalon Hybrid 12V batteries were expensive, trouble-free and lasted 7 to 10 years. Sure looks like the 12V battery in the RX350h is simply too small, likely a cost cutting move.

 

My 9.9 HP Mercury outboard trolling motor uses a 350 CCA battery! I have to believe that some engineer went by the book (displacement x 1.20) to get CCA and then the bean counters said they'd save $30 bucks with a smaller battery. I wonder how large a battery one could fit in that space?

 

The 20hr 60 A-H rating means that the battery will supply 3 amps for 20 hours before falling to 10.5v.. (60 divided by 20)

I believe that the fact that the battery is only half-charged in normal service is a much bigger deal than the nominal rating. Our 60 a-h battery is actually closer to 30 in normal service. Throw in random excessive parasitic discharge and (eventually) sulfation induced loss of capacity, and it's a recipe for dead batteries.

 

The 12v battery in the hybrids doesn't have to supply a large current to a starter motor so the old displacement x 1.2 rule of thumb doesn't apply. It only has to power up the electronics. The traction battery starts the ICE. The relatively low CCA for A-H capacity leads me to believe it's actually a deep-cycle battery. A typical 60 A-H battery will provide 650+ CCA.

 

Wouldn't a deep cycle battery not have these issues? I don't use them, but a lot of boaters do for the audio systems, etc.