why dose my car battary go dead
could be a duff 1 or the alternator could be drawing charge back through a duff zenner diode
A diode by definition is a device that allows current to flow in one direction. A Zener diode is a diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage. Zener dfiodes are not used in automotive alternators. --- The battery could be losing voltage due to a parasitic drain. Here's a video explaining it and how to find it. https://www.youtube.com/watch?v=KF1gijj03_0
A lot of things can kill a battery. As I don't have the exact year of the car I'm going to take give you a few things to check. First of all have you battery tested to make sure it is up to the task of holding the parasitic loads this car has. if it checks good then here is a list of what to check next. Glove box light, make sure it turns off, if in doubt remove the lamp, trunk light same thing, underhood light also, interior lights and there is a lot of them, vanity mirror lights, stuck brake lights switch. If all of the lighting check out then you will have to check for excessive draw on the battery, like alternator diodes bad, stuck relays, alarm system. This can get involved. Good Luck
One of the most common things I see is one of the lights under the rear view mirror gets turned on when adjusting the mirror and this drains the battery.Check those first. Next disconnect the alternator wiring and check for an excessive drain.....do not confuse the small drain needed for "on star" and other computer related items.Generally a 12 volt test light put between the positive battery post and the positive battery cable with the cable disconnected from the battery should glow dim (normal)but not brightly. remove fuses one at a time until the test light glows dimly. (keep the doors closed and disconnect the under hood light if needed) Dim light OK Bright light DRAIN Disconnect the battery completely for a day or two,reconnect and see if it is still charged. Dead battery.......time for a replacement. Good battery......keep looking for a drain!
The Cadillac should have the battery saver function that will shut all circuits down after twenty minutes if a light was left on. It will not shut off the cigarette lighter circuits so don't leave anything plugged in with the engine off.
It could be an internal short in the battery. Try disconnecting the negative battery cable at night and see if the battery is flat in the morning.
How often do you drive the car? If it sits for extended periods of time the computers in the car will kill the battery. Disconnect the negative (-) battery cable if you plan on not using the car for more than about a week. HTH. -Jim
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