recent years, the electronic content in vehicles has multiplied several
times over. More electronics means more demand on the battery and
charging system. A weak battery or low system voltage due to a charging
problem can cause all kinds of havoc with the on-board electronics.
example, low voltage may cause the airbag or ABS warning lights to come
on. The turn signals may not blink normally when the switch is flipped
to either side. Electronic gauges may give strange or erratic readings.
The engine may lack power, misfire or stall. Any of these things may
occur if the battery is low or the alternator is not producing its
normal charging output.
Many so-called battery problems are not
the battery, but a charging fault. The alternator’s job is two-fold: to
supply current for the vehicle’s electrical system and to maintain the
battery at full charge. Normally, the battery is only used to crank the
engine, to provide power for lights and accessories when the engine is
not running and provide supplemental power when the demands of the
vehicle’s electrical system exceed the output of the alternator.
alternator’s output is lowest at idle, and increases with engine speed.
The powertrain control module in most late-model vehicles controls
charging output, so the PCM can boost the charging curve a bit when
demands are high at low engine speed. Even so, most alternators can’t
achieve maximum output until engine speed reaches about 3,000 RPM or
higher. Consequently, if the engine is left idling for a long period of
time with the headlights, A/C, defrosters, radio or other accessories
on, it can overtax the charging system and drain the battery.
cars are murder on alternators and batteries because they spend so much
time idling with high electrical loads on the charging system (lights,
radios, heater or A/C, etc.).
If the battery is low when a
vehicle is first started, it takes some time for the charging system to
bring the battery back up to full charge. It might take 20 to 30
minutes or more of normal driving to fully recharge the battery.
battery technology is actually ancient. But it is simple,
cost-effective and generally provides an adequate power for most
automotive applications. But automotive lead-acid batteries must be
maintained at or near full charge for the cells to last. If the battery
is allowed to run down or discharge excessively and is not fully
recharged within a few days, the lead plates inside the battery can
become permanently sulfated. This will reduce the battery’s ability to
accept and hold a charge, and drastically shorten the battery’s life.
average service life of a conventional lead-acid car battery is only
about four to five years, and typically a year or so less in extremely
hot climates. Gel-cell batteries that do not contain liquid acid
electrolyte are better in this respect because they are less affected
by evaporation. Even so, their average service life is typically five
to six years depending on use.
BATTERY POWER DRAINS
a vehicle to sit for a long period of time without being driven (say a
week or more) can allow the battery to run down. The electronic modules
in today’s vehicles draw a small amount of power from the battery to
keep their memories alive when the vehicle isn’t running. Many go into
sleep mode and shut down after a certain period of time to reduce the
power draw, but others (such as the antitheft system, keyless entry
system and PCM keep-alive memory) are always on. Because of this, the
key-off power drain can be fairly high in many late model vehicles (80
milliamps to several hundred milliamps). This can run the battery down
fairly quickly if the vehicle sits for long periods of time, is driven
only infrequently or for short trips, or has a weak battery or low
charging system output.
Abnormal key-off power drains can also
run down a battery. Leaving the lights on can drain a battery fairly
quickly. Interior lights, or a trunk or underhood light that fails to
go out can also sap power from the battery when a vehicle sits
overnight. Sometimes a power relay may stick on, or a module may fail
to go to sleep after the engine has been turned off, causing a higher
than normal key-off power drain. Any of these can run the battery down
and increase the load on the charging system when the engine is first
started. The result can be a chronic undercharging condition if the
vehicle isn’t driven long enough to fully recharge the battery, and
shortened battery life.
Any problems in the charging system
itself can also allow the battery to run down and/or shorten battery
life. A bad alternator, voltage regulator, faults in wiring harness or
PCM voltage control circuit, or even a slipping alternator drive belt
can all cause low or no charging output.
output of the charging system can be easily checked with a voltmeter
while the engine is idling. The actual output voltage produced by the
charging system will vary depending on temperature and load, but will
typically be about 1-1/2 to 2 volts higher than battery voltage. At
idle, most charging systems will produce 13.8 to 14.8 volts with no
lights or accessories on.
If the current produced by the charging
system is not sufficient to recharge a low battery, the battery may
never achieve full charge. This can lead to a permanent loss of voltage
capacity inside the battery as the plates become sulfated.
current (amperage) produced by the charging system is also important to
maintain a fully charged battery. Not long ago, an 80-amp alternator
was considered a high-output unit. Now, alternators that produce up to
120 to 155 amps are used in many vehicles. The current output can be
measured with a charging system tester, or on a test bench if the
alternator has been removed from the vehicle.
ratings can also be given in watts (which is volts times amps). Many
alternators in foreign vehicles are rated in watts rather than amps.
The important point here is to make sure a replacement alternator has
the same power rating (in amps or watts) as the original so the
charging system can maintain the same power output as before, should
the alternator need to be replaced.
If your store has a bench
tester or a portable charging system tester, you should always
recommend testing a customer’s alternator if their battery keeps
running down, is dead or has failed prematurely. This can prevent
unnecessary battery warranty claims if they buy a new battery only to
have it run down or fail due to a charging fault.
need to be tested for two things: state of charge (a base voltage
measurement that shows if the battery is low or fully charged), and
capacity (a load or conductance test that checks the condition of the
plates inside the battery).
Connecting a voltmeter to the
battery’s positive and negative terminals (key off and all lights and
accessories off) will reveal the charge level of the battery. A reading
of 12.66 volts indicates a fully charged battery. If the reading is
12.45 volts or less, the battery is low and needs to be recharged.
batteries have a built-in “charge indicator.” A green dot tells you the
battery is 75 percent or more charged. A dark indicator (no dot
visible), means the cell is low and the battery needs to be recharged.
A yellow or clear indicator tells you the electrolyte level inside the
cell is low and the battery needs water. If the battery has a sealed
top and water cannot be added to the cells, do not attempt to recharge
the battery. The battery must be replaced.
If a battery is low,
use a charger to bring it back up to full charge. Alternators are
designed to maintain the battery charge, not to recharge dead
batteries. A heavier than normal charging load on an alternator may
overheat and damage the diode trio (rectifier) in the alternator,
causing it to fail.
When charging a battery, do not turn the
charger on until after the charger has been connected to the battery.
Sparks can be very dangerous around a car battery because lead-acid
batteries give off hydrogen gas, which is highly flammable. Also, if a
battery is frozen, do not attempt to jump it or recharge it. Remove the
battery from the vehicle, bring it indoors and allow it to thaw before
Slow-charging is usually better than fast
charging. Fast-charging saves time, but risks overheating the battery.
Slow-charging at 6 amps or less develops less heat inside the battery
and breaks up the sulfate on the battery plates more efficiently to
bring the battery back up to full charge. “Smart Chargers”
automatically adjust the charging rate. Most start out with a charging
rate of 15 amps or higher, then taper off the charging rate as the
battery comes up.
The time it takes to recharge a battery will
depend on the battery’s reserve capacity (RC) rating, it’s state of
discharge, and the output of the battery charger. The charging rate (in
amps) multiplied by the number of hours of charging time should equal
the reserve capacity of the battery. For example, a dead battery with a
RC rating of 72 will take about 12 hours to fully recharge with a 6 amp
TESTING BATTERY CONDITION
test will tell you if a battery is good or bad. The test is done by
applying a calibrated load to the battery and noting how much battery
voltage drops. The test requires a carbon pile load tester, a volt/amp
meter (if not part of the load tester), and a battery that is 75
percent or more charged. If the battery is low it must be recharged
prior to load testing.
The test requires loading the battery to
1/2 of its CCA rating for exactly 15 seconds. This is done by adjusting
the carbon pile setting on the tester. The battery must maintain a
minimum post voltage of 9.6 Volts at 70 degrees F during the test to
pass. If the voltage drops below 9.6 volts, the battery is “bad” and
needs to be replaced.
A faster and easier method to check the
condition of a battery is to use an electronic battery conductance
tester. Conductance is how much current the battery can conduct
internally. Conductance is determined by sending an alternating
frequency signal through the battery. The main advantage with this
method is that the battery does NOT have to be fully charged for
accurate test results.
battery tests bad, or it will not accept or hold a charge, it will have
to be replaced. There is no way to rejuvenate an old sulfated battery
or a battery with internal shorts, opens or cell damage.
replacement battery must be the same group size (dimensions and post
configuration) as the original, and should have the same or higher Cold
Cranking Amp (CCA) rating as the original battery. Most V6 and V8
engines require 600 CCA for reliable cold weather starting. Many diesel
pickup trucks have a dual battery setup for added cranking power, so if
one battery has failed it is usually a good idea to replace both
batteries at the same time.
Replacing a battery in some vehicles
can be difficult because of the battery’s location. It may be sealed up
inside a fender panel (many Chrysler cars) or in the trunk or under the
back seat. If the vehicle is a hybrid, it may require a special gel
cell 12-volt battery rather than a wet cell lead-acid battery. Also,
use extreme caution around high-voltage hybrid batteries. Follow the
vehicle manufacturer’s safety precautions. The high voltage hybrid
battery is usually covered by a 10-year warranty and is a dealer-only
Here’s another precaution that is often
overlooked: Disconnecting a battery that still has voltage can wipe the
memory in some modules in many late model vehicles. The resulting
memory loss in the affected modules may prevent certain systems from
functioning until a special relearn procedure has been performed (some
of which may require using a scan tool to reset the module).
prevent unwanted memory loss in modules, connect a “memory saver” to
the electrical system before the battery is disconnected. These devices
typically plug into the cigarette lighter or power outlet, or attach to
the battery cables, and use a 9-volt battery to supply power to the
modules. Another option is to connect a low amperage (3 amps) battery
charger to the battery cables while the battery is being replaced.
extra careful when reconnecting battery cables to not reverse polarity.
Reversing the connections can damage the battery, charging system, and
on-board electronics (including the PCM). Except for some antique
vehicles, all modern vehicles have a negative ground electrical system.
The negative battery post is marked with a minus (-) sign, while the
positive battery post is marked with a plus (+) sign. The battery
cables may be color coded red for positive and black for negative (but
not always, so watch out!).
Finally, batteries should be fully
charged before they are installed (to reduce the initial load on the
charging system). Batteries are “dry charged” at the factory, but can
discharge over time as they sit on the shelf. Your battery inventory
should be arranged so your oldest batteries are the first on the shelf,
with the newest batteries in the back. Use a voltmeter to check the
charge level on your batteries, and use a charger to bring any low
batteries up to full charge before they go out the door.
customers should also be reminded to check the condition of the battery
cables on their vehicle. A new battery can’t crank the engine normally
or maintain its charge if the battery cables are loose, badly corroded
or undersized. Watch out for cheap replacement battery cables that have
undersized wire inside. It takes heavy gauge wire to handle all the
amps that many starting systems require.