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Why is My Car Battery Dead Overnight?
Why is My Car Battery Dead Overnight?
A car battery is used to store electrical power in reserve to be used when the
car engine is started. Several conditions can occur that will cause a battery to
lose its charge overnight. There are several "live" electrical circuits that can
draw electrical power from the battery when the key is in the off position. Follow
the troubleshooting guide below:
Car Battery
- 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 using a battery charger. Once the engine is running
test the alternator
in the charging system. If the alternator fails, replace it with
a new or rebuilt unit and re-test system, if the
alternator tests ok proceed to the next step.
- 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 solved. If
headlight switch is off proceed to next step.
- Inspect the interior illumination lights (dome light) when all the doors
are shut the interior lights should go 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 letting you know when the switch is activated. Deactivate the
switch and re-test dome light operation. Some cars have a delay sentinel that
will leave the interior light illuminated for a preset amount of time and is
used for safety reasons. If this delay mechanism fails it can leave the interior
light on 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 ok proceed to next step.
- 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 stop. 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 and reinstall when repaired. If player tests ok proceed
to next step.
- Inspect the glove box illumination light, in most cases this light is controlled
by a small pin switch. If this switch malfunctions or is misaligned it will
allow the glove box light to stay on draining the battery down overnight. To
check for this condition look for the light inside the glove box through the
small cracks in the glove box door. If this light is illuminated when the glove
box door is shut replace or readjust the switch to operate properly and recheck
light operation. If it tests ok proceed to next step.
- 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 when the
trunk lid is nearly shut. If the light doesn't go off replace or readjust the
switch and recheck operation. If it tests ok proceed to next step.
- 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 ok proceed to next step.
- Inspect the cigarette lighter in both front and rear passenger
compartments, remove the lighter unit and look down inside the light socket.
You are looking for debris that can cause an electrical draw like a penny or
a 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 tweezers.
(Note: sometimes when inserting tweezers or removing debris from the
cigarette lighter a fuse can blow, if so replace the fuse with new after the
debris has been removed) If the lighter is ok proceed to next step.
- Inspect the electric seat control switch, 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.
- 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 the
battery has on it when the car is locked up, with the key in the "off"
position". First open the hood and disable the under hood illumination
light, if equipped. Next, with the key off and the doors locked wait 15
minutes, then disconnect the battery cable on the negative side. (The 15
minute wait allows the computers to go into "sleep mode" and shuts down all
electrical). 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.
For exact specific repair procedures for any of the steps above visit our
online repair
manual page.
Troubleshooting
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Why is My Car Battery Dead overnight?
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