wrinkle

Are you being sarcastic ?

Sure, you do not want any overcharging, but you also do not want undercharging, having to jump-start, and damage to the battery so that it needs replacement every 6-12 months, correct ?

And being forced to sit around in the car or have the car run sitting (wasting electricity or gas, and your time) for 30 minutes, just so you can charge the 12 V everyday... yup, you must've been sarcastic

StefanoS

Huh? Please explain how charging the 12v battery is damaging it.

LeX2K

I suggest you look at the graph again and pay attention to voltage.

StefanoS

See post #35 above. There's a link to the battery monitor that I purchased on Amazon. You download their free app and you can monitor your 12v charge.

wrinkle

I think you both are saying the same thing - that the charging voltage is too low, during the driving phase, to ensure that the battery is getting charged. Therefore, driving around and generally using the car as intended, doesn't necessarily ensure the 12 V battery is getting adequately charged. Which leads to the gradual chemical degradation of the battery over time, leading to needing jumpstarts, and more than usual battery replacements - a vicious cycle. This was the conclusion by lsft as well from his measurements with his 2022 NX450H+.

wrinkle

Its becoming increasing clear that the App/communication is a significant cause of the drain, given your and SMartin's investigations.

In case you take your car to the dealer, StefanoS, please share what they say. Yours is a particularly interesting situation, since you actually tended to the 12 V battery by trickle charging proactively (which I never did), and your battery still needed jumpstarting.

I'm waiting this out until I need another jumpstart, before I take it to the dealer in a battery-dead condition - so that they have a smoking gun. Or wait until my 6 month service in June, when I will complain and ask for a battery replacement and "vigorous battery test" documentation with technical details of the results. Given my battery resting voltage is consistently 11.9x Volts, and 2 needed jumpstarts, I'm fairly certain at this point that the battery will need replacement - in order to have reliable car.

LeX2K

Voltage swings going below 12 volts over and over is very hard on a battery. If that data is accurate (no reason to think otherwise) the charging algorithm needs to be fixed.

StefanoS

The battery monitor supposedly has a 1 mA draw. I only used the jump starter on one occasion and that was prior to installing the monitor. Since that one occasion, I have been using the trickle charge only periodically. I have two NOCO's, one of which is a 1 Amp and the other is a 5 Amp. The 12v seems to fluctuate from 12.2 to 12.8 currently.

wrinkle

And your NX450H+ has NOT had any problems, correct ? Looks like this problem is worse for the RX450H+, since it has more sensors/bells/whistles, and newer.

StefanoS

The NX450h+ has the same battery issue however, it is used primarily by my wife and she does drive around more than I do. Both batteries still lose charge on a daily basis but, I have not had to jump start the NX.....yet.

StefanoS

I have not yet been back to the Lexus dealer with either of my two 450h+ models. I did an oil (Mobil 1 0w16) and filter (GenuineToyota) change this weekend on both of them. I will most likely do another one on my own prior to the Lexus oil change at 10K miles. I'll wait until they notify me about the second fob on the NX and kill two birds with one stone. They already notified me on the RX but, I haven't made the appt yet. BTW, for any of you that haven't changed your oil and wish to do so, it is a very simple process on these models with the A25A engine. The drain plug and oil filter are adjacent to each other, right above the access panel. I drove the front wheels up on ramps, which works very well. The drain plug is right at the back of the oil pan so, so gravity does it's thing nicely. It could not be easier.

winpakbob

Couldn't agree more about your experience with the oil change. As someone that has always done my own on many vehicles over the past 50 years, this oil change is by far the easiest, cleanest, quickest experience I have ever had. Literally, less than 20 minutes once you have it on the ramps.

WellsB

I killed our RX450h+ battery last weekend. I was trying to get the digital key to work on my new phone and kept powering the vehicle off and on while attempting to get it to work. I tried to remember to press the brake each time, but I'm sure I forgot a few times. Thankfully, when the vehicle started acting odd, I pressed the hatch release button and it released, though I had to manually lift it. It turned out that my jump-starter was dead, so I used my high-capacity charger on 20 amps to jump it and then put it on my BatteryMinder at 8 amps, overnight to charge it back up. I tested the battery after charging it and it doesn't seem to have suffered any degradation from the episode.

The vehicle then went a week without use and started fine on the next use. I do plan on getting one of those monitors to be able to see what voltage it is without having to leave the charger pigtail hanging out.

wrinkle

Given how proactively careful you are with the 12 V battery, WellsB - if you are able to kill it, then I suspect 100 % of the 5th Gen RX 450H+ will eventually end up killing it one way or another

Curiosity question: Did you happen to take any voltage readings at all during this episode, at the failed/degraded state - or when you started out with the battery minder perhaps ? I'm curious to know what exactly is the "dead" voltage of the 12 V battery, from the perspective of the 450H+ computer.

Its good to confirm that one can jump the car with 20 Amp current, as that matches what one would expect from a hybrid/PHEV without a starter motor.

At some point, given Lexus won't do anything since 2022 when the NX450H+ started having this problem - I'm really interested in learning if there is anything we can do along the lines of a larger reserve capacity battery than the stock/OEM one (paid out of pocket). AGM batteries seem to need a slightly larger (0.5 - 0.75 V) charging voltage than the usual flooded lead-acid that is the RX450H+ stock/OEM (and its replacement from dealers that one can get under warranty) - so it seems an AGM may not be drop-in replacement that actually reduces the probability of a dead battery to near zero in any reasonable situation. That said, Odyssey does advertise an AGM for a 2023 NX450H+ despite the potential larger charging voltage need - so I'm not sure if Odyssey somehow reduced the charging voltage need to match the Lexus OEM battery for NX450H+. Understood however that the real problem is the charging algorithm that only Lexus can fix.

I'm not set on an AGM though, and even a regular lead-acid that reduces the chances of a dead 12 V situation significantly would be necessary, longer term. Its just very annoying/problematic to have to deal with this "risk" constantly (even when carrying a jump starter) - especially if/when is traveling out to national parks and such remote locations whether may not be even a possibility of any trickle-charger.

WellsB

If I recall correctly, the voltage was around 8v when I hooked up the high capacity charger. I waited a minute or so before trying to start the vehicle, and I think the voltage was up to 11v when I started the vehicle. The voltage quickly climbed over 13 on the vehicle charger.