Hybrid doesn't need a large battery it only powers 12 volt devices, does not crank the engine.

Glad I found this thread. My battery died two times. First was at a car shop to install PPF. They left doors open for a while I assume.
Second time was in my garage while I was playing with my immobilizer setting. I kept turning on and off the ignition for maybe 15 minutes or so.

Also, I am glad to found out here that the negative ground is nowhere the battery is. I kept using the bolt and luckily didn’t fry my electronics.

Since then, I have changed the settings for lights to the minimum setting.

Hi,
I experienced the no power event as well with my RX500h.
The tow truck driver that boosted me informed me that he sees a lot of this with hybrids in my city (Victoria B.C.) where we make a lot of short trips at slow speeds. The electric motor is driving the vehicle a lot of the time in that situation. Therefore, because the 12 volt battery is charged by the IC engine , it is not being charged enough. Cold weather would exacerbate the problem. He suggested that if I was not driving a lot that I should consider using a trickle charger every 2-4 weeks or use one that automatically turns on or off.
I checked with Lexus service and they agreed.
Seems to me that a "low battery" feature in the vehicle would be useful.
Cheers

I don't know about the RX500H specifically, but in the RX350h and RX450h+, the ICE has no role in charging the 12v battery. If the system is in "Ready" mode, then the 12v battery charging system is on, regardless of the ICE running or not. I'd be surprised if that was different for the RX500H.

I'm beginning to suspect that the problem is that the hybrid charging system simply doesn't fully charge the 12v battery, and that the combination of poor charging, high parasitic loads and accessory loads leaves the 12v battery dangerously low for short trips.

The 500h is a " parallel" hybrid system as opposed to most other Lexus hybrids which are "full" hybrid systems. While the full systems have 2 separate power sources (i.e. an ICE and electric motor(s)), a parallel system's primary power comes from the ICE and an electric motor is inserted between the engine block and the gear box.
The 500h does not charge the 12 V system directly i.e. with an alternator but does so through the system for charging the hybrid battery. The 500h hybrid battery is charged by the ICE and regenerative braking.
When driving with only short trips the system does not have time to recharge the 12V battery, thus the original recommendation stands.
The 500h needs to be driven at highway speeds occasionally if being used primarily for short trips or recharged by a trickle charger. The estimated time to recharge a fully depleted 12V battery is about 1 hour at highway speeds.

I can't imagine that the 500h charging system requires highway speeds to properly charge the 12v battery. That's an alternator requirement. It sounds like the 12v charging system is similar to the other hybrids, in that it draws from the traction battery. If so, then it's just time it needs, not any particular speed. Even sitting still in Ready Mode should do the trick. The 12v charging system takes only a tiny fraction of the energy that the drive motors take, so it could run for an hour and hardly draw the traction battery down.

That said, you are correct to recommend periodically charging a 12v battery with a charger, as vehicles, even when driven routinely for an hour or more, rarely fully charge a lead-acid battery. I charge all of my lead-acid batteries monthly, and find that they last over 10 years as a result, even in my motorcycles.

Keep in mind that it takes about 4 hours to charge a lead-acid battery from fully discharged to about 80% charge at the maximum safe charging rate. That is why it is critical to put a fully discharged battery on a charger as soon as possible. A vehicle charging system simply won't charge it in a reasonable timeframe, in normal driving.

Just passing on what I was told by Lexus service .

The battery and everything completely failed when I came home and parked in the garage. The crazy thing is that the car was still on and in park. All of a sudden the infotainment screen went blank and the instrument cluster began to show a message saying that the parking brake would now disengage. Then, each of the doors one by one started to lock. This cycle kept going and going. I could not exit the car. The car would not stop and the doors would not get out of the lock cycle. I tried to manually exit the car but I could not as the car doors kept locking. The odd thing is that I have never heard this "lock" thump in the car ever. Usually, this is silent. After 30 minutes being trapped, I managed to time the exit of the emergency exit lever and exit the vehicle (in between the locking cycles). It was already late at night; so, I went to bed. Upon checking on it in the morning, everything was dead. Currently waiting on a tow to the dealership.

I've owned over a 18 ICE cars over the years and I've rarely had to put a charger on a healthy battery, (since my old junker day back in the late '60s) only at the end of its life. At that point I just jump it and go get a new battery.. Now I think these Lexus hybrids might need the boost but I get 4-5 years life out of my my batteries in the Texas heat and sometimes cold.

My friends hybrid Accord got 5+ years out of his 12v battery with no issues until end of life. I know that's not the same animal but it has all the bells and whistles. .Sometimes he does 20 short drives before any real hiway speeds.

I'd like know how many 350H owners do not have any battery issues.

Just to be clear, I do the monthly charge as preventative maintenance to keep the batteries in the best health, not because they are acting weak or dead.. Most people I know get around 5 years out of a battery. I usually get 10 or more.

Did you purchase and install the maintenance charger or did the dealership do the work ?
I am looking to do this same thing but have not found a in-line fuse holder like the one you used.
Do you know where the fuse holder was sourced from ?
Thank you in advance, DEL92

Hi Del92, I provided the parts as I had already purchased the trickle charger and had the dealer install. The cable assembly came with my charger. As this a known issue they actually stock trickle chargers and cable assembly to the battery. The other option was a OEM installed trickle charger that allows you to charge direct into a receptacle mounted in the bumper for $556 CAD.
https://www.lexus.ca/lexus/en/mainta...us/accessories
Cheers

Is there a circuit breaker that protects the 12v system from the 'Jump Pad' located in the fuse box ?
I'm trying to wrap my head around why the vehicle remained disabled after the road service technician connected their jumper cables to the Jump Pad.

Recently experienced a discharged 12 v battery following a 45 minute drive on the freeway to a nearby event. Lexus Roadside assistance was very responsive and arranged for the dispatch of a local service provider to address the 'dead battery' situation.
The service technician was apparently not too familiar with Lexus RX350h models. The technician accessed the jump pad located at the fuse box for attaching the positive cable. They seemed to be at a loss where to land the negative cable. They tried landing their negative cable at several different places on the engine in close proximity to the fuse block. The first few times they landed their negative cable, there was a sizable spark and the circuit breaker protecting the service vehicle's power tripped open requiring the technician to reset it. On the third time, the circuit breaker remained closed when the jumper cables were landed, but it appeared there was no power getting to the 12v system and the vehicle could not be started. I requested the technician use his voltage meter to check we had 12v at the Jump Pad. He verified we had voltage at the pad. In the end I had to have the vehicle towed to my local Lexus dealer for repairs. They reported needing to replace the battery (under warranty) but had no explanation why the 12v distribution supply couldn't be recovered when the voltage was present at the Jump Pad.

I agree with everyone who is about to respond "the negative cable goes to the bracket to the right of the engine." From reading the Owners Manual I understand the bracket to the right side is the intended landing point for the negative cable. It's to bad the road service technician wasn't more familiar with this point.

Any feedback or comment if the 12v system has a circuit breaker between it and the Jump Pad.

Thank you for your time and considerations,
DEL92

My 12v battery was dead today, after I had returned from a four day trip to Palm Springs. We took our gas hungry Sequoia on this trip, as we towed our travel trailer for this brief getaway. I moved the RX when we returned on Friday. Today when I approached the car, the door would not open. I used the mechanical key in the fob and as expected, nothing happened when I hit the start button. I opened the hood and connected my NOCO Boost XL GB50 to the point in the fuse box and the ground. The engine started right up. I have never used anything other than "READY" mode in either of my two 450h+ cars. I had already pre-wired a battery charging harness to the 12v, as I have read of problems that others have had. I had previously charged the 12v on two occasions, using my NOCO Genius 5 charger, in an attempt to keep the 12v battery up to snuff. All of my trips in town have been in EV mode and longer trips in HV mode. Needless to say, I was a bit surprised to see this occur, as I've been fairly religious, since my purchase of this car last October, in trying to maintain the 12v unit in a good state. I don't have any other items wired to the electrical system that might be causing a parasitic draw on the battery. The 12v in these cars is a very small unit and I am wondering whether it should be replaced with something a bit beefier. Others have had their Lexus dealer install a larger CCA battery, under warranty and this may be the way to go.

I'd be interested in knowing the cause of the 12V failures.

I've owned a Prius for 15 years now and not one single time has it ever gotten a discharged 12V battery...except when we forgot to turn off a light.

I use Dr. Prius to check the voltage of the battery, so maybe I'll start monitoring it daily to see whether something is draining the thing. I mean, we do know the car has sensors all over (just going close to the car with the fob switches on the handle lights). It also is connected to the net, even while not started.

ps. We sometimes go on week-long or more trips (e.g. cruise or travel abroad). If this happens, it's good to know I can start the car remotely to charge the 12 V (at least until 2027, when I need to pay for it)