I have a '99 LX 470 with 232K and pretty much, other than a starter and a battery is 100% original. I did the starter couple years ago. Last year, my wife (who is the primary driver) started complaining about a dead battery at completely random times. Mostly, when someone had the radio on. Since the original was over 10 years old, i figured it was going bad and bought a new one. Problem stopped. until a couple weeks ago.
I was working on her truck putting on a seat cover and had the door open and radio on for maybe 30 min. I couldn't start the truck. put it on a charger and its been fine. couple weeks back, my wife was sitting reading a book with the dome light on waiting on one of my kids for maybe 30 min. no start. last weekend, i pulled all the connections and cleaned them well (didn't really have any corrosion anyway)
All seems to point to the battery. However, like what was happening before I replaced it, it would also no start almost immediately after stopping somewhere. like TODAY (while i am away travelling). My wife came home, pulled into the garage, went in the house for maybe 10-15 min and came out, no start, dash backlighting is flashing. had her check the battery, was 11.9v and, a couple min later 12.1v. I know voltage and capacity are different, but this doesn't seem logical because as soon as a jump start happens, it's all fine again. I have a full Lexus service manual but haven't scoured it yet. Is there some type of capacitor or something in the ignition side that could prevent the current flowing properly? I am not a great electrical whiz but I am stumped so hopefully someone on the forum will be able to help.