Hi, I have the same problem on my 2006 RX400h. the battery kept training too. It started 1 month ago that the car not start so I jumpstart and start for one day. I took the battery to Autozone to test, they told me that yes the battery was dead. I replace a new battery and it worked for 2 weeks. now when I left overnight, I have to jumpstart to start the car. The conclusion was pretty convince from the searching of the web that the cause is the alternator because it didn't charge the battery. So on 4/2/24, I called Lexus's service for a quote to replace the alternator. on 4/3/24, Lexus return my call and said that the Lexus RX400h does not have an alternator. They told me the Lexus has the regenerative that charge the 12V battery, and normally the regenerative does go bad. if I to replace the regenerative, it will cost $7-8k. They told me if I want, the dealer can diagnoses the problem for $258.
