WellsB

The battery in question is OEM, 8 months old and tests out as very close to new condition.

Lexus-SSA

Could someone remind us if this battery issue is mainly with the 450h and not with 350h?

waldhaus1

You are correct. I jump started it and it ran after that. The problem seems to be that when running on EV ode the 12 volt battery doesn't get recharged adequately.
Need to use trickle charger whenever I plug in the traction battery. Seems like a not well thought out design.

WellsB

The 12v charging system does not adequately charge the battery, regardless of the mode the vehicle is driven in.

EV mode is actually better than HV mode because the 12v battery is trickle-charged while the traction battery is being charged, but it's still not enough.

Roader

Dealer has informed me they opened a case with the factory and suspect the DCM. Asked me which remote functions I'm using the app for, who is my carrier, and have I added or deleted any users or changed my account using the app. In my case, I only use the app to lock the doors during charging (mainly to shut up the notifications from the Lexus app on my phone that the car is unlocked), carrier is Verizon, and no changes made to account. Expecting more info from them soon.

For those of you using a BT battery monitor, how did you go about connecting it since no access to battery terminals?

// RX 450h+ purchased 5 weeks ago

WellsB

The battery is under the rear cargo area, under a pop-off plastic panel. It's easy to get to.

StefanoS

This is the monitor that I purchased and attached to the 12v's in both of my 450h+ models. They seem to work well and send me a notice to my cell phone when the voltage drops to a low level. As WellsB pointed out, the 12v is under the cargo cover at the right rear of your RX. I hope that your dealer comes up with something positive so we all can put this issue to rest.

chuckNX

This whole thread is astonishing to me.

You guys have more patience than I do. I would be pursuing lemon law before I went through all this crap with the batteries. You must really love the car to put up with this nonsense.

Overburn

Not sure if it's mainly with the 450h but I've had this happen to my 350h

wrinkle

I suspect there is sunk-cost fallacy at play for some, like me For others it might be a bit of religious devotion, to Lexus

More seriously, I found that this problem exists in the 4th Gen RX's as well, and of course for the 2nd Gen NX - reported in those respective subforums, where people installed AGM batteries to fix it for good. I'm hoping for pioneering explorers here would find a DIY solution like that and report back!

jctscz

My solution ...attach quick connect to battery terminals ... - cable runs into edge of trunk and get a 12v charger to connect and use it every time after i completely recharge the big battery..

wrinkle

Yes, many folks have drilled holes into the car for their 12 V charging cable as well.

That approach doesn't work for me, because I only signed up for hybrid battery charging when I gave my money to Lexus. Not an additional charging/cable attachment daily for the 12 V battery charging chore. The latter is an unacceptable path for me, simply for the privilege of owning a Lexus. Hence if I have to use a band-aid, it would rather be an AGM battery or such eventually - assuming Lexus will never fix the charging algorithm at their end, despite wide, statistical prevalence of this problem as evident in this forum and on reddit forums.

alextv

Just a thought here but if changing type of battery away from oem like agm I would get Lexus dealer something in writing stating it would not void warranty. There is something strange that only Toyota knows how this charging system actually works. There is probably a delicate balance which in the end maximizes mpg.

wrinkle

They would never do that - because their "corporate script" is that they will only replace with the exact same battery (Ampere-hour, type), and will parrot that bureaucratic BS. SMartin has tried and failed already, as he reported. So he drilled a hole in the car for the 12 V charging cable, I think.

Yes, from a design perspective, you may have hit the nail there. They, by design or possibly "looking the other way", simply crippled the 12 V charging - because providing sufficient charging ability to the 12 V subsystem might have reduced their MPG ratings with EPA, and therefore affected their business plan ($$). Or it could have simply been an incompetent engineering of the 12 V charging subsystem design that was copied/pasted from the Rav4 Prime, without any regard to the enormous number of sensors, data telemetry and useless vanity frills ("illuminated door sills") that we we have in a Lexus. You see how the problem is worse in the 450H+ than the 350H (both in RX and NX lines), as the 450H+ are more loaded with sensors and factory-fit options like "illuminated door sills", irrespective of we want the latter or not.

And so, we are holding that bag now.

StefanoS

As I understand it, a flooded lead-acid battery is charged at 13.8 to 14.4 volts and an AGM battery requires a charge of 14.4 to 14.9 volts. Charging an AGM battery at a lesser charge level will greatly shorten it's overall life. I am certainly not a battery expert but, I am not certain that I want to stick an AGM battery in either of my cars just yet. I am still going to wait until the mothership gets this resolved. Latest news may indicate that it is the DCM module causing the issues.