I have also used ACC mode in the past with no issues. But this time it was different. After just a few mins, I first received a message stating there was an issue with the parking brake. This was followed by numerous warning lights on the dash. I tried to turn off the car... Nothing. I tried to restart normally. Again, nothing. At that point the electronic doors stopped working and I had to open them manually. I made the mistake of closing the door, and could not re-open it. Off to Google to learn how to manually open the door. There were no warnings that the battery was running low. One second it was fine, the next was a cascade of errors and failures. I went in to tell my wife that my car went bat **** crazy. Then I remembered this thread and headed off in her car to buy a jump box.

 

Did you change the battery? Was it bad (i.e. load tested)? Often a single cell in a LA battery will go wonky all at once.

 

I was away from home the month of November and came back to find our 2023 350h battery completely dead. Got the car started after jumping it and drove it for an hour to get the battery charging. All seemed well for about a month but 1,000 miles later it just did it again yesterday. Jumped it again and took it straight to Lexus where they said the battery was shot and they replaced it under warranty.

The dealer told me to remove the battery connection next time if I am away for that long because the hybrid 12 volt is smaller than a non hybrid. Is this true? My other non hybrid car is a 2021 model on the original battery and it started right up.

 

My 500h only has a single medium-sized 12V battery (in the trunk). My previous vehicles all had two 12V batteries and usually larger. So I do think Lexus is going with the "minimum necessary" to save weight/size/cost considering the 12V system doesn't have the load of starting the ICE.

I've left my vehicle for a week at a time and it's been okay. But if you're leaving for a month it is probably good insurance to get a battery tender.

 

Tons of complaints on this forum about the batteries on the 350h. My 12V died when I listened to the radio for 10 minutes with engine off. The hybrid battery died for no reason later and had to be replaced. The dealer told me they are having to replace batteries every year in these cars, they now test them at every service. Disconnecting your battery is a ridiculous suggestion.

 

The issues folks have reported regarding the 12v battery have been enlightening. When I google "EV 12 volt battery dying" I was astonished at the numerous issues with 12v batteries across most hybrid and EV brands that have been occurring for years. I was not aware of how ubiquitous the issues are. I am clueless as to why manufacturers cannot seem to get this right. Furthermore, most of these vehicles are connected to the Internet. How hard is it to have a voltage monitor on the 12v battery that sends a message to your phone warning of low voltage or charging needed? It seems many people are left stranded with no early warning to prevent the dead battery issue. I can only deduce the combination of short driving patterns, more electronic technology in vehicles constantly drawing power, and smaller batteries seems to be a recipe for disaster.

 

These newer cars have so many computers & electronics that over time, they will drain a battery from sitting. I have battery tenders on EVERY auto, motorcycle, mower & piece of equipment I own for when it will not be used for more than a week. It works.

 

I stumbled across this video which explains the 12v saga very well in simple terms.

 

The 12V battery unexpectedly died in my 500h a little after 1.5 years of use. It was never parked more than a week without driving. Lexus replaced it under warranty. If it was a non-hybrid vehicle, Lexus Roadside Assistance would have replaced the battery on the spot. It was only jump started.

 

Was away for the holidays for 10 days. My '23 RX 350H (20K miles) was sitting in my work (heated) garage.

Returned to find car battery completely dead.
Waited 3 hours for Lexus roadside assist (aka AAA) who never showed up, alerting me to one delay after another...
Good Samaritan security guard finally offered me a jump and I was on my way, but man did that stink after an early 3 hour flight.

Guess I will visit the dealer and see if I need a new 12V based on these comments. Real drag for a 1.5 year old lux. vehicle. sigh.

 

Exactly what our fav Lexus Service Advisor told us. And we do the battery tender, as well. Which our advisor even recommended.

 

My concern is not that Lexus won't replace the battery, its more that this is going to happen every 1-2 years and eventually we'll have to pay a price out of warranty. Is there a stronger battery that is suitable for this car? I would strongly recommend not having AAA jump it, they may jump it incorrectly as my Lexus adviser later warned me and fry the ECU. Just keep a battery jumper (it's like $40 at costco for what seems like a good one) and learn how to jump it yourself. Keep it under a seat or something (not in the trunk because that will be tougher to access in the event of a dead battery)

 

I have already resolved to purchase a $70 battery minder/charger (Noco Genius 5) - that can be wired to my trunk battery with a quick release connector - and when I travel for a week or more, I will just plug this in back in the trunk to keep the battery from fully discharging...
From what I have read even a larger, stronger battery may not hold up against the draw of the background hybrid systems.

On why discharge is happening:

On installing the Noco Genius 5: (ps the 'too small' battery connect leads mentioned can be drilled to be made large enough..)

 

With proper engineering there is zero reason that a vehicle should not be able to be started after several weeks sitting outdoors in cold weather, turned off. The first video is being far too kind - engineers designing the vehicle are being paid to calculate reasonably anticipated battery drains (factoring in that cold weather occurs, decreasing capacity) and select a proper battery, software engineers are supposed to write/test decent quality code, QC staff are supposed to monitor suppliers (and the car manufacturer's own processes). With good low-power vehicle monitoring computers, and good low-power sensors to sense key proximity, and the vehicle only doing minimal modem connects when it's turned off, and over-the-air updates only being done when the 12V battery reports a decent state of charge, the vehicle should still have sufficient power to turn on.

Why cars aren't able to be started:
-Sloppy charging algorithms - the hybrid system isn't topping off the 12V battery often enough, or stopping before the 12V gets to a solid state of charge (SOC). If the charging algorithm is only bringing the 12V to say 80 or 85% SOC, but the drain calculations for the 12V battery are done as if it's starting from 100% SOC, there will be problems.

-Poor transportation practices. A few car manufacturers are good about transportation, having transport modes that act, in effect, like disconnecting the battery terminals during the possibly-multiple-month evolution from when a car leaves the factory to when it arrives at the dealer. Otherwise, even if everything else was done "perfectly", after multiple months of expected parasitic drains a vehicle's 12V battery may be at-or-near failure (capacity reduced due to sulfation occurring). The car may still be able to be jumped, or put on a charger, but the battery capacity may have been significantly reduced (e.g., a 50AH battery is now a 25 AH battery).

-Sloppy onboard software design. The "unintended" parasitic drains due to bad software can exceed the total expected parasitic drains that the engineers designed for. Examples include things like leaving a vehicle CANBUS network alive (when it should be off), the vehicle "phoning home" (doing status stuff using the cellular modem) far more often than was planned, overall computers/sensors being left powered-on when they are supposed to be turned off.

-Bad battery supplier QC. Batteries have specs that the car engineers use in sizing things. Some historically very-highly-regarded brands have obviously been cutting corners, new batteries dying sooner than they should. The car manufacturers are supposed to perform QC auditing of suppliers, identify/resolve issues when parts supplied to them aren't up to snuff.

-General design "cheaping out". It's entirely feasible to monitor the 12V battery. A device like the Ancel BM300 Pro draws a trivial 1mA current, can be bought retail for only $25, would undoubtedly be cheaper for a vehicle manufacturer to acquire when looking at 1000s of units. A few times a day a vehicle computer could poll it for voltage/SOC, report out if the SOC is low. Bonus points for them to have more frequent polling while the vehicle is running (and the 12V battery should be getting topped off), display voltage/SOC on a widget available for use on the infotainment system.

-Poor dealer handling of their inventory, poor pre-delivery checks. Cars that are on the lot need to have their batteries topped-off periodically, using external chargers or even just turning them on and letting them run for a half hour to an hour. Pre-delivery checks (when a vehicle has been sold) should include good battery checks, including battery capacity, not just seeing that the car will turn on.

Net, it's car manufacturer design/production/QC/cost-cutting that's responsible, not something magical about hybrids.

 

This high tech device has no issues keeping a battery charged correctly yet Lexus can't code their PCM to do the same.