Two comments . Too bad you can’t charge through the 12v cig lighter socket. And I hope this isn't a problem for the 2025 NX 350h I’m about to pick up in a couple of weeks.

 

It's been a while since my previo us posts, so here's a recap: Brand new NX450h+ that died and would not start within first few hundred miles. Dealer said "You're not driving enough." So we trickle charged 12v (accessory) battery often, but still had dead battery even after long (hours) drives. Back to the dealer again, this time the 12v battery was replaced. Couple weeks later, it's acting the similar, except now seems worse...dying overnight even when fully charged during the day. So we resigned to just keeping it on the trickle charger and even having my wife leave the car running while locked and parked at the market.

Then we went on an overseas trip when we parked (very securely with the LAX Hilton valet) at the airport for two weeks. We were prepared for a dead battery with a fully charged jumper in the back seat. We also asked valet to park the car, leave it running, and lock it up. This would give about another hour of charge to the 12v, albeit at a lower level because of accessories running while it was charging, but locked. About 3 day into our trip, the Plad Tech theft-recovery system installed by dealer alerted me to a battery level below 12v. Then the next day, Plad Tech alerted that the voltage. was 0. No surprise, we were expecting that.

Returing from our trip, when I picked up the car I told them I believed the car was dead (they said that was common and had a jumper). I said I had a jumper and could accompany the valet to help open car and jump battery. So we went together into the basement parking to retrieve our car.

Then the surprising thing happened. The valet used the fob to unlock the car. I was stunned! The doors unlocked and we got in and IT STARTED! After two weeks and after Plad Tech said the battery level was 0. We had some issues with the HUD freezing and the lane departure function was barely noticeable but we made the three hour drive home with no other issues.

After returning home the car was behaving as it had been before our trip; i.e., dying on a daily basis if not on the trickle charger. We also contact the dealer, again, and reported the issues we were having, arranged service, and asked them to keep the car for however long it takes to figure out the problem because this was already the car's second battery. We got a loaner.

The dealer did a load test on the 12v, found it insufficient, and replaced it (again, now on the 3rd one in < 3,000 mi.) the day they got the car. I told them this was the third battery and to please do a thorough test for parasitic drains. They kept the car six more days to monitor it (I was keeping track too, with Plad Tech app) starting it every morning then letting it sit. They said there were no other notifications or faults shown during their diagnosis. After getting the car back (three weeks now) there have been NO issues. We've not been using the trickle charger nor letting it run in parking lots. The Plad Tech app reports the battery between about 12.4 to 12.8 volts, regardless of the short trips we drive.

I have no explanation how it was able to start after weeks at the airport!

Your thoughts are appreciated.

Cheers!

 

I just went on vacation and was monitoring the 12V battery while I was out. The drain after 7 days is extremely low, which could be the reason why it can start.

 

That may well be, but it doesn't explain the battery being reported less than 12v on day three, then dead (0 v) on day 4, yet 10 days later it was able to start. No trickle charging. No remote starting to charge for 20 minutes. The valet did not try to start car or move it during this time. How could the battery regain enough charge to limp along for 10 days and be able to open doors and start the car?

I appreciate that after about a week sitting the car goes into "deep sleep." But this doesn't explain going dead and coming back to life.

 

AFAIK that "Plad Tech" tracker connects to OBD port and can only report voltage sent to the port, not on the 12V battery directly. It may be not accurate if the ECU goes into some sleep mode, or the tracker goes down because of low voltage.

 

True. Plad Tech is probably not as good an indicator of 12v battery health as sticking a meter on the battery. But the point is that Plad Tech was reporting a dying battery, which was consistent with the recent history. The question of how the car started 10 days later, when it couldn't last more than a couple days at home, is the real mystery.

We expected it it die within a day or two being parked at the airport. That was its past behavior. We were prepared for it with the jumper on board. We got notified by the Plad Tech app that it died. As expected.

Where did the energy come from to allow the car to operate doors & lights and unlock and start 10 days later? It should have been dead as a fart due to any on-board monitoring for app or fob signals, etc.

Is there some algorithm to leak some juice from the traction battery to the 12v during hibernation?

I don't know.

 

It makes Plad Tech the suspect. Many such gadgets have cut-off voltage when they kind of shut down to prevent complete discharge of 12V battery. Then if it's sloppy programming, it may not distinguish between true 0V and hibernating gadget.
Normally you would check amperage a gadget uses, but as it's on OBD port, and usage may fluctuate when it connects to cell network, I don't know how to do it in practice. Other than get battery voltage monitor with history and compare voltage drop patterns with and without Plad Tech. E.g. it may keep constantly pinging CAN bus and keep the car computer awake when it would normally sleep.

Then there was a fix for Lexus App recently that supposedly fixed abnormal 12 V drain for some other plugin owners. Maybe it was just at the time.

 

I read about the 12v issues with Lexus before I bought my 2025 NX 450+. I was mildly concerned, but really did not consider it to be an endemic problem with Lexus. Anyway, this past Sept, we left the Lexus for 2 weeks in our garage, and when we returned it started just fine. The traction battery was fully charged and other than the parasitic drain from the on board electronics, it just sat there. What we did do was disconnect the car from the phone app and our home wifi. Don't have a clue if that had any affect on battery drain.

 

Two plausible reasons:

RX's, and I think likely NX's too, have key proximity sensing over bluetooth for keyfobs for various functions - which is why we keep our keyfobs in faraday pouches at home, to prevent drainage of the 12 V battery. At the airport, your keys would have been too far from car to have woken it up. The fob has to be at least 10 feet away from the car to not wake it up from sleep. I had my RX450H+ last 26 days without a dead battery at home when I went overseas, but then the temperature dropped 1 week later, the battery had died - because I hadn't driven much that week after returning - not enough to charge the 12 V, and it was before I had bought my trickle charger.

There is a report by an RX450H+ in the RX forum that his "paired EV charger" was interfering with his RX's sleeping mechanism and killing his 12 V battery. This was also at home obviously, and he removed such interference to prevent the 12 V discharge.

 

This is interesting. Do you know any more about it?

Thanks

 

https://www.reddit.com/r/Lexus/comme...mment/lqlw6i2/

 

Actually, monitoring just the battery voltage does not tell you the amp-hour capacity left in the battery. Just saying you may not be monitoring what you think your are.

The battery size is measure in AH ( Ampere Hours). Lexus recommends 60Ah or higher; measuring voltage does not measure this.
The battery size is recommended to have 345 CCA (Cold Cranking Amperes) ; measuring voltage does not measure this.


Good Luck

YMMV,
MidCow3

 

I know this is mainly the NX450h+ everyone is talking about but I have this problem with my 2024 NX350h. My battery has died twice and granted I don't drive it every day but I don't go weeks without driving it. I haven't taken it to get the battery replaced and maybe I should.

Couple questions I have noticed as I bought the NOCO Genius 2D.
1. Is that a good choice as it comes with the eyelets instead of the clamps?
2. I tried connecting it to the 12v in the trunk but when I tried to start the vehicle it acted like it was dead and this was minutes after driving around town and had just turned the vehicle off. I had Lexus Roadside come jump it and he noticed it acted like it was dead too but then he placed my key fob next to the start button and it started right up. Is this a required step after disconnecting the battery?
3. Should I have Lexus replace my battery?
4. I keep my keyfobs and key card in a faraday box so it's not connecting and reconnecting all the time.

 

You might want to check your keyfob battery.
If the 12V battery died twice, you should go to your dealership and have it checked. If you are under warranty they could replace it under warranty.

​​​​​I've personally installed a Noco 5D charger and have my battery replaced by the dealership as well. I have a few videos talking about the 12V battery and monitoring now it charge the 12V.

 

Any more thoughts on this thread. I see the last post was November. Going away for 3 weeks. Thinking might need to buy a trickle charger for the 350H
Been looking on amazon