1991 Lexus LS 400 BATTERY DIES AND CAR SHUTS OFF WHILE DRIV

Get the battery and alternator load tested-one might not be putting out the other is not taking it.

The battery had a full charge that day....we had put it on a charger a couple days earlier and it started everytime i tried it during the next two days....it wasn't until i drove it that it died.....how do u get the load checked and what does that mean?

Alternator load check is where you apply resistance by using a rheostat to it for a given time/speed to make the alternator throw out its maximum current output. Same goes to the battery applying a given current draw for given time such 15secs to check whether the battey will hold 9.6 volts in that time.

All you need to check both is a voltmeter

The battery should read an open voltage of 12.6 and up volts.

Alternator while vehicle is idling should be within 2 volts from the open voltage of the battery if its charging the battery.

Thank you so much! I will try this as soon as possible...I found out today that the battery and alternator are both still under warranty so I will be able to replace them if needed....thank you for your advice and I will let you know how it works out....