BATTERY DISCHARGES WHILE IDLING - 1999 Lexus ES300, 220k miles, owned since 2001 and totally happy with it. A little worried that I am now only a traffic jam away from being stranded. So far, I have a new battery, alternator, and starter. No fuzes blown, No parasitic draw. Started this issue a year ago and I only recently connected random and infrequent dead battery to extended idling. Now the condition is easily repeatable - Idling with AC and headlights (automatically on) will drain battery down to 10 Volts in about 30 minutes. Charges fine at 1200 rpm and, of course, while driving. Idle speed is normal and stable. Car is perfect otherwise.

 

Same here on my 2000 ES. Happened to me several times. I did have my Torque scanner connected one time and noticed that while the engine was idling smoothly, the charging rate fell to 8 volts and hovered there. I had to replace my oem alternator a year ago and since then, that one failed and the current a/m one has done the same low charging at idle as well. I'm almost convinced a/m replacement alternators are the problem. Just this past week, I purchased a 2006 ES 330 so I'm not trying to fix that issue but I told the new owner of the issue and if a solution is posted, I'm going to pass the info along. Good luck.