To clarify, my 3rd battery solved the problem.

 

I would never assume a battery is bad just because it died, nor insist that a battery be replaced if it tested as good. That is a knee-jerk reaction and an indicator of a parts-changer, rather than a skilled mechanic.

Our battery died twice. Neither time was the battery at fault, and it tested good both times, after being recharged. It hasn't died again, since.

 

What was the cause of the battery dying?

 

The first time was due to leaving it in ACC mode too long. The second time was due to excessive parasitic draw. I believe the parasitic draw was due to the keys being stored too close to the vehicle. I've not seen a similar draw since moving them 30' away.

 

-edit-
I figured out what ACC meant. Duh.

 

The ACC mode will drain your battery FLAT in an hour, documented.

Thankfully, our dealer emphasized the need to have our 500h Hybrid in READY mode when listening to the radio or setting up defaults.

 

Can you share the brand/make and Ampere-hour rating of the 3 batteries, or at least those details of the latest and currently working battery you got ?

 

Yep. I'm pretty sure that's what I did. I sat in the car for hours reading the manual and going through the whole system. I (stupidly) thought that the traction/hybrid battery was supplying the power.

 

My dealer said the same when I experienced this issue a while back. Perhaps it is a setting (or the software version), mine (RX350h) automatically turned off after 10 minutes (It displayed a message that system is being turned off to conserve battery). Or maybe it turned off because the battery was getting low!!

I definitely recall the situation because mine ended up with all sorts of system malfunctions after the car was jump started. I posted this in System malfunction error on dashboard - Page 4 - ClubLexus - Lexus Forum Discussion (post #49). Battery issue is one thing but ending up with all sorts of system malfunctions is a lot more frustrating for me!!

 

My '17 RX 350 non-hybrid also automatically turns off from accessory mode, putting a message up on the infotainment screen before it does so, though IIRC it may be after something like 20 minutes.
(since then we carry a portable radio for drive-in movie watching).

The '17 has zero issues running just the radio, at low volume, for a long time, plenty of battery capacity, no parasitic issues, but it would protect against a case like someone trying to run a high power device off of the accessory socket.

 

I've left our 350h for three weeks and no issues upon return.

 

Yeah. Well, the new RXs apparently require as much power as the Transformers. I think I need to go and find the All-Spark.

 

The sad part is the urban legend that is developing about the underlying reasons behind this problem, which for the most part have no relation to the batteries or EV/HV mode, while being misinformed by the dealers, and NOT being addressed correctly by Lexus. Even the Service Advisor at my 5 K appt, who was responsible and helpful in every other way, did not know that the problem is the charging algorithm, and instead had advised me to run the car more in HV mode.

 

Unless someone really pays attention, they'll never realize it's the charging algorithm, and specifically, when the vehicle is being driven, is the issue. If one just checks while the vehicle is sitting in park, they'd never know there is an issue.

 

I too would have thought that running it in HV mode would more likely charge it than EV.
Where might I find some information about this charging algorithm?