User Manual

22
Battery Testing — Voltmeter
Unlike Conventional batteries, AGM types cannot be tested
using a hydrometer because they are sealed. Instead a
voltmeter can be used to perform an open circuit voltage test.
The test can be used for both Conventional and AGM batteries.
The test is used to determine the following: battery state-of-
charge, ability to hold a charge and shorted or open battery
cells. It is possible that a battery can pass the open circuit
voltage test and still be unable to start a vehicle and battery
load testing will be required to determine if the battery needs
replacement. Before performing an open circuit voltage
test the battery must be fully charged.
Charging a battery using the vehicle’s charging system or a
battery charger creates a “surface” charge across the battery’s
cells. The surface charge needs to be removed before an
accurate test for open circuit voltage can be performed. To
remove the surface charge, turn on the ignition key for about
three minutes then turn it off. Now let the battery sit for about
10 minutes. This step is not necessary if the battery has been
sitting for 1 hour after charging is complete. Connect a digital
voltmeter to the battery, red lead to positive and black lead to
the negative battery terminals. Open circuit voltage indicates
what percent of charge the battery has reached after charging.
Open circuit voltage for a fully,
100% charged AGM battery is
12.8 to 13.0 volts. AGM batteries that are 75% to 100% charged
will measure
12.5 to 12.8 volts. Conventional batteries have
slightly lower open circuit voltages:
12.6 volts (12.8 volts with
Sulfate Stop) for
100 % charge and 12.4 for 75% charge..
If after charging, and the open circuit voltage indicates that
the battery is less than
75% charged, the battery is probably no
good and should be replaced. Before the battery is condemned,
try charging it again. If the battery is still not close to
100%
charged it needs to be replaced. The open circuit voltage test
is not conclusive. It is possible to have a
100% charged battery
as indicated by the open circuit voltage test that will not start
a powersport vehicle reliably. A load test must be performed to
determine actual battery performance after charging.
Charging System Quick Check
A quick check of a powersport vehicle’s charging system can be
performed using a digital voltmeter. Connect the voltmeter leads
directly to the battery (red to positive and black to the negative
terminals). Read the open circuit voltage and start the engine.
Operate the engine between
3000 to 4000 rpm while watching
the reading on the voltmeter. If the vehicle’s charging system
maintains voltage between
13.0 and 14.5 volts, the charging
system is probably working properly. If voltage is the same as
open circuit voltage (usually less than
13 volts) the charging
system is not working and further diagnosis will have to be
performed. Installing a new battery in a powersports vehicle with
a faulty charging system will eventually result in a dead battery
and an unhappy customer. Always use the OE service manual as
a guide for further testing and diagnosis of the charging system.
Battery Load Testing
Once the battery is charged and passes the open circuit voltage
test its time to determine if it can really perform its main job—
starting the engine. It might seem obvious that if the starter
button is pressed and the engine starts, the battery must be
OK. While a marginal battery might start an engine a few
times, it may not reliably start it in the future—especially in
cold weather.
There are two tools that can be used for load testing: a dedicated
battery load tester, or a digital voltmeter. The load tester can
be used when the battery is not installed in a vehicle. The load
tester simulates the electrical load of a starter motor to load-
test the battery. These testers are usually used by dealerships
and are able to adjust the load applied to the battery under
test. Always follow the instructions that apply to the specifi c
battery load tester. In general, apply a load of three times the
ampere-hour rating. After
10 seconds check the battery voltage
with the load still applied. A good
12-volt battery will not drop
below
9.5 volts (ambient temperature of 70° F). A 6-volt battery
should drop no more than
5.25 volts. If the voltage reading is
below these minimums replace the battery.
As an alternative to the load tester, the vehicles starter
motor can be used to provide the load to test the battery.
To load test the battery, cranking voltage must be measured.
Low cranking voltage will indicate that the battery is getting
tired and should be replaced. Following are the steps for
performing a battery load test using a digital voltmeter and
the vehicle’s starter motor.
Connect a digital voltmeter directly to the battery—red lead
to the positive terminal and black lead to negative. While
watching the voltmeter, press the start button and crank
the engine’s starter (it’s OK if the engine starts). Just before
the engine starts, note the voltmeter reading. As the starter
motor places an electrical load on the battery, cranking
voltage will normally drop. If battery voltage drops below
9.5 volts (at 70° F) while the engine is cranking over,
the battery needs to be replaced. If the engine starts too
quickly to read cranking voltage, the ignition or fuel injection
computer fuse can be removed. This will allow the starter
motor to operate (without the engine starting) and cranking
voltage can be measured.