Need to replace you car battery? We are a team of ASE certified mechanics
that will show you how to do the job correctly while saving you money, or at
least see what you are paying for when taking your car in for repairs.
What Goes Wrong?
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 each
of the batteries 6 cells and can happen in about three to four years of the
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
Step 1: Remove the Battery Cables
Though appearances may slightly vary 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 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 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
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. They should 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
Battery Replacement Video
Watch our video which gives you an idea on what you are in for when replacing
your car battery.
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.
Battery Charging and Testing
Voltage from the engine's alternator maintains the batteries state
of charge. This continuous cycle can produce electricity for three to four years.
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
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.
How a Battery Works
The car 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 stores electrical energy to start the engine and operate accessories
in the electrical system throughout the car when the
engine is not running. A battery is equipped with a positive and negative terminal from which
two cables are attached. These cables route power from the terminals to positive power distribution
center or fuse panel and negative power to the engine block.
The old assembly is completely recyclable contact your local recycling station,
autopart store or repair garage to dispose up properly. Do not discard batteries
Store a battery fully charged in a cool place and off of the ground
Check the battery every two months and recharge if needed
Remove all electrical connections from the battery
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.
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.