Dear Auto Advisor,
My husband is a “do it yourselfer” and wants to fix my 1996 Cadillac. The problem seems to be that the battery goes dead when I need the car the most. So far this week I have been late for work twice, one more time late and I am unemployed. The battery is new and the alternator is working according to the parts store. Please tell me what I can do to solve this problem.
Jackie, having a car not start is not a good thing in our society. Having a car that is dependable is a valuable asset. Having one strand you is a liability in your life and creates way too much drama. What I am going to suggest is for you to seek professional help (automotive professional help). Having a new battery and a good charging system is only the first step. More than likely you suffer from a “parasitic drain” on your battery. This can be from the air ride suspension coming on in the middle of the night. Or any number of reasons that may cause this condition of a dead battery.
To prove that the car has a parasitic drain that is causing this problem you will need to make sure that you have a fully charged battery that reads 12.65 when you shut the car off at night. (If your husband does not have a digital volt meter he will need to get one)
Now you need to disconnect the battery for the night. The next morning you will need to check the battery voltage again. It should read the same as it did the previous night. If the car battery voltage has dropped, say to 11.5 volts. Then the new battery is defective. If the voltage is still 12.65 then you have a parasitic electrical drain on the battery.
To find this problem you will need to find a shop that can isolate the problem circuit. The shop you find should have a low amp clamp and a lab scope and the ability to reprogram the computer if needed. I know from experience the acceptable drain on your battery should be 50 milliamps or less after everything on your car has “timed out”. If a shop only uses the old tried and true “test light method” then they are not keeping up with today’s electronics. It takes more than 500 milliamps to make a test light “slightly glow”. 500 milliamps will drain a battery down in about 2 to 3 days if left alone and not driven.
Hopefully I have not confused you and this will help you figure out your problem. If I have confused you, come by my shop and I will hook up my lab scope and tell you if you have a parasitic drain or not. That part is free, finding the parasitic electrical drain is another story.
Live long and prosper.
Return to frequently asked questions