I bought a 07 is250 with 93k miles from the original owner bought from the Lexus in my town and has all service records. It has a 550cca battery and I got it inspected just last week before I insured it
It was driving perfect until yesterday, the day before I got a oil change and filter done at Toyota and they said my air filter is good. I drove around 100km that day and parked it at my friends house for a few hours 6.8 degrees so kind of cold (it’s normally parked in my heated garage). I leave and start it up and everything’s normal let it warm up then drive 10-15 minutes and park for a few minutes. I noticed nothing up to this and I saw my touch screen was just black and then my car turned off. It turned on pretty rough and some of my electronics were tripping out and then I turned it off (not sure why). It didn’t turn on after that and showed VSC light and battery, luckily my friend was there with boosters and it turned on. At first while driving my steering was really tight and could barely turn but once I got out of the lot it was fine and I drove it 10 minutes home it drove fine and I went up too 100km/h. I’m pretty sure it’s the alternator because I turned it on today and it started a little rough and the vsc light was still on and my tranction control was off and wouldn’t turn on

 

Yes sounds like it's charging at very low voltage. I had the same exact symptoms but no dash lights. I cought mines early because I have a pretty powerful sound system and the alternator couldn't keep up. It tested fine at AutoZone 3 times. Finally I took it to my audio shop and they said it was charging at 9 volts. Pretty much nothing. Drive it to AutoZone one more time and it ruined my battery and finally tested bad.

 

Autozone is hardly an authority on anything related to cars. One time I took a car to autozone that had the check engine light on. They told me that I had code P0308 - misfire on cylinder 8. The car was a 6 cylinder. And the problem was a solenoid valve in the evaporative pollution circuit P04 something something.

 

I agree that sounds like the alternator is bad. Many of the same symptoms you mentioned happened to me as mine was going out.