Mechanics

Battery Goes Dead Overnight

Step by step repair guide on how to fix a car battery that goes dead overnight. This article pertains to all non-hybrid and electric vehicles.

Difficulty Scale: 3 of 10

Tool and Supplies Needed

  • Small plastic tweezers
  • Test light
  • Protective gloves and eyewear
Before you begin park the car on level ground, in park with the emergency brake "ON".


Car Battery

Step 1 - If the alternator has failed it will allow the battery to go dead, if the alternator tests ok proceed to next step. Visit - Alternator testing

Step 2 - This first test is simple but you would be surprised at how many people simply leave their headlights "ON" overnight. If the battery is dead check the headlight control switch. If the switch is in the on position turn the switch off, and jump start or charge the battery. The battery should re-gain its state of charge after about 15 minutes of driving and your problem will be solved. If headlight switch is in the "OFF" position proceed to the next step.

Step 3 - Inspect the interior illumination lights (dome light) when all doors are closed completely, the interior lights should turn off. If the lights stay on check the headlight interior light bypass switch located at the headlight switch. This switch is designed to illuminate the interior lights indefinitely when the doors are closed and is used when people are left inside the car and need light for a particular reason. To check the headlight interior light bypass switch turn the headlight control knob fully right then left, you should feel a small bump in the operation while rotating informing you know when the switch is activated. Deactivate the switch and re-test dome light operation. Most cars have a delay sentinel that will leave the interior lights illuminated for a preset amount of time and is used for safety reasons. If this delay mechanism fails it can leave the interior lights on while draining the battery. If this is the case the interior light delay sentinel or body control module will need to be replaced. If all tests okay, proceed to next step.

Step 4 - Inspect the car stereo tape deck or CD player, sometimes a tape or CD will get stuck in the player either loading or ejecting causing the motor inside the tape deck to keep running. This small motor can draw enough electrical power to drain the battery overnight. If a tape or CD is stuck in the player try using a small flat bladed screwdriver or small tweezers to remove the culprit. If the stuck tape or CD will not come out. Remove the player and disconnect the unit. Once the unit has been removed either replace the player or send it to a stereo repair shop, reinstall when repaired. If player tests okay proceed to next step.

Step 5 - Inspect the glove box illumination light, in most cases this light is controlled by a small pin switch inside the glove box door frame. If this switch malfunctions or is misaligned it will allow the glove box light to stay on draining the battery down overnight. Check for this condition in darkness while looking for light inside the glove box through the small cracks in the glove box door seal. If the light is illuminated while the glove box door is closed, replace or readjust the switch to operate properly and recheck light operation. If it tests okay proceed to next step.

Step 6 - Inspect the trunk illumination light, in most cases this light is controlled by a small pin or a mercury level switch. To test the trunk light operation observe the light as you close the trunk lid, the light should go off as the trunk lid is nearly closed. If the light doesn't go off, replace or readjust the switch and recheck operation. If it tests okay, proceed to next step.

Step 7 - Inspect the hood (covers the engine) illumination light, in most cases this light is controlled by a small pin or a mercury level switch. To test the hood light operation observe the light as you close the hood, the light should go off when the hood is nearly shut. If the light doesn't go off replace or readjust the switch and recheck operation. If it tests okay proceed to next step.

Step 8 - Inspect the cigarette lighter in both front and rear passenger compartments, remove the lighter unit and look down inside the lighter socket. You are looking for debris that can cause an electrical draw like a penny or an aluminum gum wrapper. Anything that can cause an electrical draw will drain the battery power. If debris is found remove it with a small pair of plastic tweezers. (Note: sometimes when inserting metal tweezers when removing debris from the cigarette lighter a fuse can blow so use caution, if the fuse does blow replace it after the debris has been removed.) If the lighter is okay proceed to next step.

Step 7 - Inspect the electric seat control switches, this switch can become sticky or weak allowing the switch to stay engaged forcing the seat motor to draw power from the battery until dead. To check for this condition observe the operation of the seat control switch if it does not return the neutral position or is sticking in one position replace the switch with new and recheck.

Step 8 - If no other electrical accessory is causing the battery to drain overnight, a manual draw check of the electrical system will need to be performed. What this means is, you will be checking the electrical draw from the battery with the key in the "off" position" and doors closed. First open the hood and disable the under hood illumination light, if equipped. Next, with the key in the "OFF" position and the doors closed (drivers side window down) wait 15 minutes, then disconnect the battery cable on the negative side. (15 minute wait allows the computers to go into "sleep mode" which shuts down all electrical systems). Attach a test light between the negative battery cable end, and the negative battery terminal. The test light should illuminate dimly or not at all. If the test light is "ON" brightly there is a strong electrical draw in the system. To locate this electrical draw start removing fuses one at a time. When the test light goes out the circuit in question has been located. You will need a car repair manual to identify all accessories in a particular circuit, repair as needed and re-check system.

Helpful Information

A car battery is used to store electrical power which is used when the ignition key is turned to the "ON" position. Several conditions can occur that will cause a battery to lose its charge overnight. There are several "live" electrical circuits that bypass the ignition switch that can draw electrical power from the battery when the key is in the off position. As a battery ages it loses its ability to hold a charge, as a rule of thumb a battery will last about three to four years. If the battery is fairly new you will need to start the engine by jump starting or charging the battery by using a battery charger.

AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-11-24)