Q: I have a 1996 Lexus Es 300. This morning on the way to work the battery light came on and the radio went off.

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I have a 1996 Lexus Es 300. About a month ago I left my lights on and it drained my battery. I received a jump and the car has been running fine until today. This morning on the way to work the battery indicator light came on and the radio went off. After a few minutes the battery light went off and the radio came back on. It kept doing this all of the way to work. When I got to my destination, I turned off the lights, heater and radio and then turned off the car. I waited about two minutes and tried to crank the car and it would not crank. Do you think that this is a problem with the alternator or do you think the problem is with the battery.

My car has 270000 miles.
My car has an automatic transmission.

I would suggest having the alternator checked to determine if it is receiving the proper amount of voltage from something called the voltage regulator. The voltage regulator regulates the charging voltage that the alternator produces, keeping it between 13.5 and 14.5 volts to protect the electrical components throughout the vehicle. The voltage regulator controls the field current applied to the spinning rotor inside the alternator. When there is no current applied to the field, there is no voltage produced from the alternator. When voltage drops below 13.5 volts, the regulator will apply current to the field and the alternator will start charging. When the voltage exceeds 14.5 volts, the regulator will stop supplying voltage to the field and the alternator will stop charging. This is how voltage output from the alternator is regulated. When the voltage regulator is not working properly, this may cause the alternator to allow the power the alternator supplies to drop resulting in the battery dying again. I would suggest having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.

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