What battery voltage are you reading on the 12v battery after the car sits overnight??

My RX was recently serviced by Lexus dealer and one of the items i wanted checked was the 12v battery(I know all about past issues) having an at rest voltage of 11.4 volts.

I went into the dealership yesterday and read the workorder and they claim all is well with the battery and it tested at 12.25 volts. I popped the hood and broke out my meter and tested for voltage at the jump points and measured 11.7 volts. I showed the service adviser the 11.7 reading and he made the comment that the voltage reading would be different at the battery, so i opened the rear hatch and tested the battery and showed him 11.7 volts. I asked him for a reason for the discrepancy and pretty much got that deer in the headlights look. I politely asked to talk to the service tech but he declined.

I wanted it all on record at the servicing dealer and I have opened a case with Lexus Customer Care.

Any one here have a 12v battery that measures 12v at rest with the car off???

 

Keep in mind that resting voltage isn't what you are seeing when a door is open or you are even near the vehicle with a key fob.

Before I installed a Bluetooth battery monitor, I would hook a charging pigtail to the battery to measure resting voltage and would let the vehicle sit for an hour before measuring it, making sure to not bring the fob near the vehicle.

That said...
It is pretty widely known at this point that the Lexus charging algorithm on the hybrids for sure, and possibly the 5th gen RX350 as well, doesn't actually charge most of the time when driving the vehicle. The only time it reliably charges is when the vehicle is on and in park, and 5 minutes after initiating a remote start. About once a month, the system will charge for about an hour.

Over time, the resting voltage of the 12v battery will drop below 12.4v, where sulfation starts to occur. When that happens, I charge the battery on a quality automatic charger. That happens about every two weeks for me.


This is covered in detail in this thread,
https://www.clublexus.com/forums/rx-...d-threads.html

The available solutions(as I see them); Disconnect the voltage sensor. This puts the charging system in "fail-safe" mode and causes it to constantly provide >14 volts, like a traditional alternator system. This has an unknown effect on the vehicle systems and some have warned that this could cause the DC-DC converter to fail on your own dime. I also have concerns about constantly charging the battery, but traditional alternator systems have been doing that for decades and continue to do that today. It's the only thing that directly addresses the underlying issue, but could cause costly other issues.


Install a Bluetooth battery monitor. This does not address the underlying issue, but does give warning when the battery is dangerouslly low on charge.

Charge the battery with a standalone charger every 2 weeks. This prevents the battery from dropping below 12.4v, which is where sulfation starts. Sulfation shortens the lifespan of a lead-acid battery. I believe this will prevent most dead batteries and premature battery failures. The timing can be tweaked using a Bluetooth battery monitor.


Carry a jump starter such as the Schumacher SL1648, which has leads that will reach the Lexus approved jump points. Familiarize yourself with manually unlocking the door and with jump startimg the vehicle. This won't solve the underlying issue, but will prevent you from having to call roadside assistance with the attendant inconvenience and delay.


Install a Ionic Emergency Start which is a Bluetooth enabled permanently mounted jump starter. This won't solve the underlying issue, but will prevent you from having to manually unlock the door and hook up a jump starter if the battery dies.

 

Its not accurate to measure it this way to get meaningful data, but I still measured under the hood and got 11.6 V.

I don't worry about the 12 V battery health at all since I have the Ionic Emergency Start - which can not only jump-start, but can also allow me to drive to the dealer/shop for a battery replacement even if my stock 12 V battery is permanently dead.

 

Life expectancies say that automotive lead acid batteries do not take kindly to being undervoltage. At what under voltage reading does the car refuse to wake?? 11.4? 11.2? 11.0? 10.8? Etc. I do know that if drops onto the 9’s, it is not going to work. Why, after daily 70 mile trips, why is the battery not at least 12v?? Lexus dealer does not know and kisses it off to being normal.

 

As I wrote before, the charging system simply doesn't charge most of the time. When you are making that 70-mile daily drive, it is not charging, it's only supplying enough voltage to run the 12v systems, not to charge the battery.

It is normal. It's the way Lexus/Toyota designed it. Of course, that doesn't make it right.

 

That's a great question - I don't believe we have hard data from anyone in this forum for that threshold of "refusing to start" condition, yet - at least not for the hybrids. For the ICE/Gas version, a forum-member measured that threshold to be 11.85 V - however, that obviously doesn't apply to the hybrids, since they have far lower current-loading requirement than the ICE, in order to start.

Lexus dealers, as an overall population and with rare exceptions, have to be the biggest sleazebags in the luxury car market of the US. The only item unknown to me is whether its their incompetence or their corrupt lies/deceptions that take the cake. I have thus far elected to not to buy extended warranty from Lexus, and would rather self-insure against problems, just to avoid having to "deal with" Lexus dealers as a primary reason.