lsft

The manual says this:
"When the vehicle is left with the AC charging cable connected, the electricity consumption amount of the 12-volt battery increases due to controls, such as the system checking, operating. When the AC charging cable is not needed, remove it from the vehicle."

I don't have the tools like you who can do the checks and would be interested to know how much it draws.

CdO

Maybe I can just hook up my multimeter to the battery; plug in the charging cable (without it being pugged into AC power); and, see what happens? I don't think the computer will be of any use.

Aloha808

Can you unplug a car's 12V battery when you go on vacation in a hybrid? Or will that cause the hybrid battery to overheat? Please ONLY comment if you know. Anyone can speculate.

lexxxxus

Tbh it’s pretty absurd that Lexus isn’t addressing this issue, leaving customers figuring out how to fix this on their own.

JasDmw

After having thought about this and reading the many replies, I realize that what I was doing was not a normal or good practice. I had the car in the "on" position, without the engine running or in the "ready" mode. Lexus did not design for this, rightfully so. When it's in that condition, all the electronics throughout the car run as if the engine/charging system was running. They have sized the battery for the optimum conditions based on how the car should operate, with some to spare, likely 5 minutes running without the engine on. If I had the car in full operating mode (ready), the battery would not have died. In this case, this is a user issue (me), not a design flaw.

I did this same thing with my 2020 RX once, in a car wash line. Thinking I was smart, I figured out how to keep the car "on" without the engine, so I could listen to the radio. In that car in accessory mode, it would shut off after I think 5 minutes. You could re-enter accessory mode I think 3 times and then you had to start the car. I thought that was a pain so I bypassed that and got away with it several times. Well, smart guy me, one time I drained the battery and it was really stuck; I couldn't start the car or disable the electronic brake. Fortunately I was close to the bypass lane of the car wash and a nice guy was able to drive up there and give me a boost.

So in fact this post is more of a heads up to everyone, if you're going to putz with the settings or whatever, more than a few minutes, turn the car on! Problem solved.

Doug007

I hope this is seen as related to the 12v issue. We traveled for 10 days and left our 22 NXH in a carpark without issue. I took the extra step as was recommended somewhere on this forum and manual to disable the key fob (holding the lock while pushing unlock twice) which eliminates the car for searching for the fob.

gcskoor

Yeah, I twice not so quickly learned "the best practice" of the 12v battery in the hybrid the hard way. LOL

I also got the NOCO GBX45 jump starter just for the worst case, my other car and to help others, since the NX should not be use to jump start another car. I also added NOCO Genius 2 charger o maintain the battery.

Tarnshoe

Is this specific to just the NX or all hybrids?

CdO

Unless the car is charging or discharging (READY) the high voltage battery is internally disconnected. You can only get juice in/out of the HV battery if 12V is applied to the the two internal 'switches'. This is why there is a 12V battery, even in EVs... safety... no 12V, no danger of high voltage. No worries disconnecting the 12V.

Related from the manual:
Observing the following can help suppress battery capacity decline...
Leave a low level of charge in the hybrid battery (traction battery) when leaving the vehicle undriven for a long period of time.

CdO

I plugged in the charging cable (without it being connected to AC power) and measured the 12V battery current.
After everything settled down it read 0.14A (~1.7 Watts).
I disconnected it; waited; it went down to 0.01A (~0.1 Watts).
Reconnected; waited, also 0.01A (~0.1 Watts).
Guess I didn't wait long enough the first time.
Switched my meter to low range... ~15mA (~0.18 Watts)

Not a definitive test; but, I don't know when I'll have an opportunity to measure after a full charge. Right after I finished, I thought I should have set the charge schedule and had the EVSE plugged in waiting for the charge to start... oh well.

JasDmw

All cars, I killed the 12V battery in my 2020 RX gasser by leaving the ignition on without the engine running.

SenorValas

I was always under the impression that if you are running the car in ACC mode (i.e. turned on but not in READY mode) and using functions such as playing with the settings or listening to audio, then the car would pop-up an alert in the instrument display warning of possible battery discharge. I know my Gen 1 NX did this and I'm pretty sure I've seen this on my Gen 2.

Maybe you missed the alert?

JasDmw

You are correct, I am referring to the conditions when you have the ignition in full on position without the engine running or in EV mode. Some settings functions don't appear to be available in accessory mode. I made the mistake of having the car in the "on" state without the engine for too long!

lexsc4

Yep, I was napping in my wife's NX350h for a good 30 minutes while waiting for my daughter, with the READY light on, the AC was on at #2. I was able to start the car no issue. Outside temp was ~80F.

Tarnshoe

My apologies. I was replying to the part where they said to not use the NX to jumpstart cars. Is that a NX issue or a hybrid issue?