Need to replace, load or draw test your battery? We are a team of ASE
certified mechanics that will show you how to do the job correctly while saving money, or at
least see what you are paying for when taking your car in for repairs.
What Goes Wrong?
A car battery is designed as a chemical reactor which uses lead plates to
generate voltage. A battery goes bad when the chemical reaction inside the
battery starts to become weak. This is due to the natural degradation of the
lead plates in one or more
of the batteries 6 cells and can normally happen in about three to four years of the
A battery can fail in one of two ways, the first way is very quickly in
others word you go out to your car and no lights will come on and the car is
dead. In this case a jump start may not even help because the battery is so far gone it just dumps (pulls
in) all the voltage supplied to it.
The second way is the battery can go bad while supplying a slow decline of voltage.
This results in slow than normal engine cranking sound that you will notice in the
morning or after the car has been sitting for a long period of time. Once you
notice this it's up to you to be preventive and change the battery before total
Sometimes a good battery will be dead in the morning because the car has a
voltage drain in the electrical system which is called a parasitic draw. This
means there is something electrical staying on in the car when its not suppose
How Does it work?
Your car battery is designed to store electrical power which is used to start
the engine when the key is turned to the crank position and engage the starter.
A battery also stores electrical energy to start the engine and operate
accessories in the electrical system throughout the car when the engine is not
This battery is a rechargeable unit in the SLI (starting-lighting-ignition)
variety which is lead acid based and is the oldest
style of rechargeable electrical supplies. These batteries are divided into 6 separate cells.
Each cell producing about 2.1 volts which when combined create up to 12.6 volts.
As the state of charge decreases the voltage
and amperage it produces also decreases. Electrical power is created through a chemical reaction where positive and negative lead plates are immersed in an electrolyte solution (acid).
This voltage is then released through the positive terminal (red) and returned
to the negative terminal (black).
A battery is equipped with a positive and negative terminal from which two
cables are attached. These cables route positive (red +) power from the
terminals to the power distribution
center or fuse panel and negative (black - ) power to the engine block and the
A non "deep cycle" battery must have a rest period or "downtime" to allow the plates inside
each cell time to cool. A battery subjected to a complete discharge will
fail prematurely unless it is a deep cycle battery. All batteries are hazardous material
and must be disposed of at a local parts store or recycle center.
If the battery warning light has been on while you have been driving the car you
will need to
test the alternator
first. This is because the battery might not be the problem if it is not
receiving a proper charge from the alternator.
In This Guide
Load testing a battery
Troubleshooting an electrical system drain
Reasons for a Dead Battery
Battery is more than three years old
The alternator is not charging or overcharging the electrical system
There is a electrical (parasitic) draw on the system
Let's Get Started
When a battery goes bad it can expel acid around the battery, battery box and
cables. This acid is corrosive and you don't want to get it on your clothes or
skin. It's a good idea to wear rubber gloves like you would use to clean your
household oven. Also, put on safety eyewear and old clothing. By sprinkling
baking soda over the battery and then rinsing it with water will help neutralize
the acid and clean the area before work begins.
Step 1: Remove the Battery Cables
Though appearances may vary slightly for each car the process is virtually the same.
The battery location will be under the hood in most cases but some cars may have
it in the trunk or under the rear seat. Record the radio stations for re-entry as they will be lost once the
electrical power is disconnected.
Using an 8mm or 10mm wrench to loosen the bolt for the negative cable
end. You might need to give a twisting motion to help remove the cable. Be
careful not to touch the wrench to the positive side of the battery to avoid
a short circuit. Always undo the negative side first because the positive side is
more prone to shorting to ground via any metal in the area. Then push the cable away to avoid it
accidently coming back and reconnecting to the
Next, undo the positive side cable this will normally be a red color and
identified by a positive sign near the terminal connection. Use a wrench or
ratchet to loosen the cable end. At this point there is no chance of creating a
short circuit because the circuit is no longer live with the disconnection of
the negative cable.
Step 2: Remove the Battery
Some manufacturers have a battery cover which now can be removed once the cables have
been disconnected. This will also allow you to gain access to
the battery hold down bolt. This cover should be cleaned before re-installation with
water and soap to remove any acid residue that might be present.
Locate the hold down bolt or J bolt nuts which are either at the top or
bottom of the battery mounting box. If the hold down is at the bottom it with only
require one bolt to be removed while a J bolt style of mount will require two nuts to be
removed. On a bottom bolt style of mount use a long extension and ratchet to
help in the removal. These bolt sizes include 8mm and 10mm. There will be a
plastic wedge piece that will also need to be removed as well.
After moving the bolts and hardware and while still using gloves grasp the
battery and wiggle it slightly to break it loose from its mount. Then hold
tight as you lift the unit from the vehicle. Brace your knees and back for this
step due to the weight of the battery. Once the battery has been fully removed use a garden hose to
fully wash the area free from acid. This will also
prevent corrosion of metal pieces and wiring which could be routed below the
Step 3: Match the New Battery
Now that the old unit has been removed compare it to the new battery while
checking the size, terminal position, cold cranking and reserve amps which
should meet or exceed the old battery.
Step 4: Install the New Battery
While firmly holding the new battery,
gently lower it into position. Be mindful of the terminal orientation so the electrical cables will
attach to the corresponding positive and negative cable.
Once the new unit is in place wiggle it to ensure it's down into the box
mount then lower the mount wedge and bolt into place. This wedge should only be
installed in one direction with the stepped part toward the batteries side wall.
Wash these parts with soap and water to remove corrosion before reinstalling
After the hold down has been
lowered into position tighten the bolt securely. At this point you
should see and feel the battery get tight within the battery box.
Step 5: Attach the Cables
Remove both terminal covers of the new battery which are used to prevent damaged and
shorting while in shipping. The terminals should now be clean and ready for the positive and
negative cable to be installed. Set the cover back into place before the cable
Use a cleaner tool with a twisting motion
which will create a fresh metal surface within the cable end to aid the
transfer of amperage needed to run the car. Take note this
cleaner has a taper fit and will only work correctly in one direction. Complete
this operation by cleaning both negative and positive cable ends. A small wire
brush will work for this as well.
Install the positive cable first, tighten the nut while holding the end
downward to help the connection. To ensure a proper installation wiggle the
cable end slightly. Never attach the positive cable to the negative side of the
battery or the negative cable to the positive side. This will cause major
electrical problems such as shorting out the alternator, main computer or other controllers inside the vehicle.
Once tight reinstall the positive cable protective cover. This cover helps prevent accidental short circuits when working inside the engine bay.
Finally install the negative cable end onto the battery terminal and tighten while
holding downward. Check the cable end for tightness by giving it a twisting
motion. Wipe away any dirt or metal shavings from the cable end cleaner and double check your work and you are all
set. Once the replacement is complete it's a good idea to
the alternator voltage output using a voltmeter. Also observe the electrical
system warning light or gauge this will ensure the operation of the alternator.
Watch the Video!
Watch our video which gives you an idea on what you are in for when replacing
your car battery.
Battery Load Test
Need to load test your car battery? We help you test your car battery without the
aid of a tester. We use this test in our shop which only takes about
15 minutes. When working with a battery wear protective eyewear and gloves. Stand clear
of the battery while the engine is being cranked over.
Step 1: Battery Test and Inspection
Open the car hood to locate the battery and check its condition (some
batteries can be located in the trunk or under the rear seat). You are looking
for leakage and bulging of the battery sides which are an indication of warped
internal plates that can short circuit. You are also looking for corrosion at
the positive and negative terminals which can eat away at the metals in the
battery cables that will cause a connection problem. To
start the battery test turn the headlights on and leave them on for about 15 minutes
(do not start the engine).
Step 2: Load Test the Battery
While the headlights are still on crank the engine over and observe the headlight bulb brightness.
The bulbs should only dim slightly when using the starter. If the headlights dim way down and go out or you notice the engine
is cranked over slowly followed by a machine gun style of clicking noise
the battery must be replaced because it cannot supply the voltage needed to operate the
car. If the battery is good it will withstand this load test.
Watch the Video!
Here is a video of the car battery load test being performed.
Battery Draw Test
Is your car battery dead overnight? We have created to help save you money by doing the repair yourself or
at least see what you are paying for when taking your car in for repairs. We
will show you the easy fixes first and then onward to the more complicated electrical
Most Common Electrical Draw Problems
Seat switch stuck
Glove box light on
Trunk light on
Dome light on
CD Stuck in player
ABS relay sticking
Side mirror switch stuck
Alternator shorted internally
BCM or GEM shorted
Alarm module shorted
Door lock switch stuck
Cigarette lighter stuck down
Vanity mirror stuck on
Scenarios We Cover
My battery is more than three years old
The car has a sulfur or rotten egg smell and is dead
I am driving the car with the battery warning light on
I just installed a new battery and it has lost it's charge
I smell something burning and now the engine wont crank over
Now that you have an idea of what could be wrong let's go into detail on how
to check for these problems and how to fix them.
Step 1: Load Check Your Battery
If the battery charge warning light was not on light the last time you drove your vehicle the alternator is
probably working correctly. If you did notice the battery warning light on the battery is
probably down on charge which is not the fault of the battery.
A sulfur or rotten egg like smell is produced when the battery is shorted
internally either from age or being overcharged by the alternator. In either
case the battery must be replaced and the
alternator output voltage checked. As the battery starts to age, three years or more, it will loose its ability to hold a charge
overnight which is the first sign the battery is ready for replacement.
It is easy to load test your battery even if you don't have a voltmeter or load
tester to see if the battery is weak.
Step 2: Check the Seat Switch
There are several "live" electrical circuits that
bypass the ignition switch that can draw electrical power when
the key is in the off position. 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. To check for this condition observe the operation of the seat control switch.
If it doesn't return to it's neutral position or is sticking in one position
seat the switch with new part which you can get from Amazon, an auto parts
store or the dealership.
Step 3: Check the Glove Box 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
light to stay on draining the battery. This can be sometimes tough to see in the
bright light of day so it's best to check during
the evening time. Look for light inside the unit through the small cracks in and
around the box door. If the light is on open and inspect the light switch to
replace it if needed or make minor adjustments to help it work correctly and
turn the light off.
Step 4: Check the Cigarette Lighter
Check the cigarette lighters in both front and rear passenger compartments.
Check to see if the lighter is stuck down which is usually accompanied by
a fair amount of heat and a burning smell. Pull the lighter upward to stop the electrical draw. In
this case the lighter has gone bad and needs replacement.
Step 5: Check the CD Player
When you shut the ignition key off the radio turns off as well. This is not true
for the CD player and changer. If a CD gets stuck in the load or eject position
it will continue to work the small motor inside the player while draining the
electrical system. With the key off while being very quite listen closely to the
player, if you hear a motor running a CD is stuck. Try to work the CD either in
or out using a small tweezers or flat blade screw driver.
If you cannot retrieve the CD pull out the radio fuse until you can replace the
unit or have it repaired this will stop the battery draw.
Step 6: Check the Door Lock Switch
The door lock switch is constantly hot or live with electrical power. Sometimes
the control switch will get gummed up with dirt or soda which makes the switch
stick in the lock or unlock position. This will force the lock actuator in the
door to stay on which will draw the battery down. Inspect the lock switch to make sure it
returns to its neutral position. If this switch is broken or permanently stuck
replacement is required.
Step 7: Check the Mirror Switch
The side view mirror switch continues to get power after the ignition switch is
off. This switch like other switches can get gummed up from grime and soda which
can hold the switch on forcing the motor to draw power. Check the switch
operation to ensure that it returns to its neutral position. If this switch is
broken or stuck it will need to be replaced.
Step 8: Check the Vanity Mirror Light
A vanity mirror which is located in the passenger or drivers side sun visor has
a light in most cases that can stick on. To check for this problem move the
visor slightly downward to observe a light that is still shining even if the visor is in the up
position. If this is the case pull the visor down to inspect the small pin
switch and repair or replace as needed.
Step 9: Check the ABS Pump Motor
The abs system will stay live when the ignition key is off in most vehicles. This
system has a control relay that is integrated into the module or in the fuse
panel. If when you have the key off and you hear something running under the hood or frame of the
vehicle it's probably this unit. Locate the fuse for the ABS system and remove it
from the fuse panel until you can
replace the ABS module with a new part.
Step 10: Check the Trunk Light
A trunk light may or may not be controlled by the car's BCM depending on the
year and manufacturer of the vehicle. The information we have found on this
subject is vague to say the least. The good news is it's extremely simply to check if the
trunk light is causing the electrical draw problem though it's best to check in
the evening time where observing the light is much easier. Pop the trunk open to
observe the light. Then slowly close the lid while watching the light through a
small opening near the rear of the trunk lid, the light should go off. If the
light stays on replace or adjust the pin control switch or trunk latch.
This section is reserved for the more obscure problems
Step 1: Check the Alternator
The alternator is used to charge the battery while the engine is running.
When this unit shorts out it can create a draw on the system. To check for this
problem wait until the engine is cold then locate the alternator and feel it
with your hand to check for warmth. If the alternator is warm with a possible burning
smell there is an internal short and the
alternator must be replaced.
Step 2: Check the BCM or GEM
The computer BCM, Alarm and GEM modules can internally short circuit which can
cause various electrical systems in the car to stay "live" which will draw
electrical power. This problem can be checked by locating the fuse of the system
and removing it or removing the controller altogether. If the vehicle starts
the next morning you have found the problem.
Step 3: Manual Draw Check
If you can't find the cause of the battery drain a manual draw check of the electrical system will
need to be performed. With the ignition key in the off position and the doors closed (driver's side
window down) wait 15 minutes. Then disconnect the battery cable on the negative
side. A fifteen minute wait time allows the computers to go into "sleep mode"
which shuts down most electrical systems.
Attach a test light between the negative battery cable end and the negative
battery terminal. The test light should light up dimly or not at all. If the
test light is on brightly there is a strong electrical draw in the system. To
locate the draw start removing fuses one at a time (doors closed). When the test light goes out
the circuit in question has been located. Identify all accessories in a
particular circuit by using a wiring schematic and disconnect them one by one
until the test light goes off.
Step 4: Check the Headlight Switch
These next set of problems pertain to older vehicles built before the year 2000
in most cases.
If you leave the headlights on overnight the battery will be 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 fifteen minutes of driving.
Step 5: Check the Dome and Interior Lights
Once all of the doors have been closed check the interior and dome lights. These lights should turn off after a short amount of time. If the lights stay on
beyond a reasonable amount of time check the interior light bypass switch
located at the headlight switch or on the bezel which also controls the
brightness of the dash lights. You should feel a small bump while rotating the
thumb wheel informing you when the switch is activated or deactivated. All doors including the lift back or hatch have a pin switch or an internal
switch located in the latch itself that detects when the door is open. When
these switches fail or become misadjusted the interior lights will stay on.
Step 6: Check the Under Hood Light
Some SUV's and trucks have an under hood light that is controlled by a mercury
switch which senses the level of the hood. At night look under the
vehicle to check for light near the engine bay. To fix this problem replace the light assembly.
Voltage from the engine's alternator maintains the batteries state
of charge. This continuous cycle can produce electricity for three to four years.
Test the battery easily without a load tester if you are not sure of the battery's
The most common way to recharge a battery besides the car's alternator is by a process called trickle charging
which is performed by using an inexpensive battery charger.
Most repair shops have a more powerful and expensive charger that
is capable of recharging at a higher rate over a shorter time period. When
re-charging a battery use caution. Always connect the charge leads while the
charger is off. This will prevent a spark from being generated. A battery is
most prone to an explosion after a recharge.
A new battery can go dead and fail prematurely if there is a
parasitic draw which will occur overnight. The system should be tested for this condition to ensure a
long battery life. If your battery has failed you can
jumpstart the car by using jump cables.
Watch the Video!
The old battery is completely recyclable. Contact your local recycling station, auto part
store or repair garage to dispose of properly. Do not discard batteries
Store a battery fully charged in a cool place and off of the floor
Recharge the battery every few months
Remove all electrical connections from the battery
Never touch a metal object between the two battery terminals to see if it is charged, this can cause
it to explode. Use caution when working with batteries because they are filled
with acid. Inspect batteries regularly if acid is present replace it and check
the charging system. Be extremely careful when handling a battery by using
gloves and eye protection.
When the battery is overcharged water in the electrolyte solution
is transformed into hydrogen and oxygen. This can cause an explosion if a spark
or another source of ignition is present near the battery.