Hello everyone,

I would appreciate some expert opinions on my 12V battery, especially from those familiar with the RX450H.

In June 2022, I purchased a 2022 RX450H, but I haven't driven it much since then. Following the advice of a UK Lexus dealer, I turn on the car's "Ready" mode for 60 minutes once a week to ensure both the HV and 12V batteries get charged, as described in this article: https://www.rrg-group.com/blog/what-...r-a-long-time/.

On a Monday in December 2022, I drove the car for hours. Four days later, on Friday, neither of my car keys could open the door. I called for roadside assistance, and a technician jumped the 12V battery. The car started. After that, I kept the car in "Ready" mode for more than an hour.

The next day, I drove the car to the dealer, and they told me that everything was normal and that the 12V battery was more than good enough. They could not replace it for free. When I asked why the battery had died, the dealer told me that it was because I hadn't driven the car enough and advised me to drive it for at least one hour a week. However, the dealer seemed not to understand that when the car is in "Ready" mode while sitting in the driveway, the ICE will charge the HV battery if needed, and the HV battery will charge the 12V battery if needed.

Afterwards, I started to monitor the voltage of my 12V battery on multiple occasions, with the longest duration being 17 days. The following is the record of this 17-day monitoring. The "V" column shows the 12V battery voltage, represented by the vertical bars on the graph with the scale on the left axis, and the "Level" column shows the 12V battery charge level, according to the table below (https://batteryspecialists.com.au/bl...g-a-multimeter), represented by the line on the graph with the scale on the right axis.

I have observed that the voltage always drops to 12.0V or lower within 3-6 days, after which the voltage drops are comparatively smaller. I park my car in the driveway, keep the car keys at least 120 feet away, and avoid using the Lexus app. I even removed the AirTags from the car to ensure that it remains in a good "sleep" mode. Every day, I open the hood, measure the voltage, and close the door, taking less than 3 minutes in total.

I have a few questions:

1) Does my 17-day record above make sense? Assuming that the car consumes almost the same amount of energy every day, the second table (voltage vs charge level) appears to be incorrect, and none of the tables I have seen online can explain the constant daily energy consumption.

2) The average voltage (about 10 readings) after charging was 12.43V if charged by HV battery and 12.67V if charged by Diehard charger (external). It seems to me that the 2022 RX450H is smarter in charging and stops charging at around 80%.

3) Is my battery better than "good enough"? Although the car started without any issue (except the incident last December), I cannot complain.

4) Any idea why my car died last December?

5) Do you have any suggestions?

Thank you
RobMot

 

To be frank, I'm very skeptical about "turn on the car's "Ready" mode for 60 minutes once a week." I think it's unnecessarily too much.

My daughter drives a 2015 Honda Accord. She lives in a college town where everything is within walking distance. Leaving the car in the garage for 2 weeks is not unusual. She's never had to jump start the car.

We have a 2002 Honda Odyssey of which sole job is to carry dirt/manure from Home Depot. During winter, at times it sits on the driveway for 2 months. Then it needs to be jump started to Home Depot and back (total driving time: 40 minutes), then it will be OK for at least the next 4 weeks.

2 months ago, the whole family went to NY for 5 weeks. When we came back, the 2020 Rx-450h and the Accord started immediately. The Odyssey (had not been driven for at least 4 weeks before the trip) needed a jump start.

So I think this incident of yours, "On a Monday in December 2022, I drove the car for hours. Four days later, on Friday, neither of my car keys could open the door." needs some investigation.

 

Your numbers are very interesting, but we don’t know how low is too low to run the system. It is not about cranking power, so I suspect your numbers might be “normal”. I had a similar event in February this year, where the car would not go to ready and kept saying that the car was not in park. I moved it in and out of park many times and finally it went to ready. The incident occurred because I left the car in Accessory mode while listening to the radio. Normally the engine starts if the battery needs to charge, but I do not remember if it ever started. Anyway, I drove the car about 2 miles home. The car did the same thing the next morning, when the temp was -20. Again, I got the message that it was not in park. It finally went to ready and has been OK since then. I suspect that the battery did not charge enough in the 2-mile drive. It is a known fact that when the battery is low, it produces random false messages. The next week I left on a 4000 mile road trip, and to protect myself I purchased a jump battery, but I never needed it and the car has been perfect ever since the 2 issues.

As far as how long can the 12 volt go without charging, You chart shows a drop to 11.4 volts, but as I said earlier it that the lowest it can go? For example, my wife has a 2016 Rav hybrid that she only drives a few times a month. This leads me to believe that the battery can drop pretty far before being an issue. My experience with AGM batteries in walk along golf carts leads me to believe that testing them is not the answer, because when my cart begins to act up the battery needs to be replaced even though it may test OK. A new battery always solves the issue in the carts. The same would seem to hold with the hybrid cars. If the issues with starting or going to ready continue, then I would say the battery needs to be replaced no matter what the test might indicate.

 

I've owned a 2020Lexus RX450h and now have a 2022 RX450h. I drive only about 4000 miles per year. I try to drive the RX every three or four days for a few miles. The owner's manual states that the battery is not charged when the car is in "N" (neutral) even if the "Ready" light is on. Lots of drain on the battery from the electronics on these newer cars.

 

@Pentaprism Thanks for your response. I agree with you, “turn on the car's "Ready" mode for 60 minutes once a week." is unnecessarily too much”.

@golferjack Thanks for your response. Very interesting golf carts experience.

@RGSW Thanks for your response. Yeh, my car is about 4000 miles too so far. 😊 I am pretty sure the car is in the “P” position when I turn it to “Ready” every week. The 12V I measured was 14.0V or higher when the car in “Ready” mode even with engine off.

 

I think how long you drive your car prior has less to do with an issue as the type of driving. If you were in slow speed EV mode and burning battery you could have turned the car off with just 2 bars left (in a low state), then the several day pause could have caused the issue. I was just looking into 12v batteries myself on my 2017. Just 35,000 miles but 6 years old. I notice after sitting overnight it has just around 12v but still 450 CCA so fairly strong reserve. I think Toyota keeps in low state of charge intentionally to preserve battery life personally, so I may just wait another year on replacing mine. Typically where I live we get around 7 years from a good 12v. Colder climates are harder on batteries as are really hot so life depends on location and use as much as anything else.

 

I just replaced the factory installed Lexus 12V battery. I replaced it with an Acdelco AGM bci size 47 battery. The new battery fit perfectly. Even the vent hole is the correct size. I used a small 12v battery connected to the jump start connection under the hood to prevent data loss during the change out. Just have to be careful not to short out the battery terminal during the change out. All is well. Car is running fine. Battery voltage stays around 12.6V.

 

Thanks for the information. I can buy those in Denver. Nice to know you can use the jumper posts to change out the battery.

 

I received a quote from the local Lexus dealer to replace my 2018 battery for 340.00, which includes installation. I might go with them because I am not sure if something else is going on. Last January the car would not start (ready light not on), but after about an hour of messing with it finally started. I had been listening to the radio in accessory mode and I suppose the battery had gone down below the minimum. The same scenario a few months later, when it would not start. I then bought a jump box, but never used it until a few weeks ago. Now it seems the car will not go to Ready if left over night. I have been using the jump box to get it going in the morning, and then it is ok the rest of the day as I do errands. To me logic says that the battery has a bad cell, but that the charging system is working correctly, because the car starts the rest of the day. In fact the car starts after only being driven a few blocks, so I assume the charging system is ok. On the other hand, it could be something else that is causing the car not to go to Ready. I believe that if I go to a parts place and have them check the battery it will show ok, because at that point it is charged. I have no way to test the battery, so I will probably get the dealer to check out the system.