results of the battery condition tests. This infor-
mation has more value than you might think,
but it requires a bit of prior recordkeeping on
your part.
When you install a new battery, perform a
conductance test on the first day of the battery’s
service life and log the CCA. This measurement
will be your starting point, or benchmark.
Then periodically test the battery and log the
results. Generally, batteries don’t fail suddenly,
but deteriorate gradually. As your battery ages,22 electrical systems troubleshooting
your log entries will show a gradual decrease in
available CCA. By tracking the CCA lost over
time, you will establish a trend based on your
boat’s actual use. This will enable you to make
an educated guess as to when battery failure is
imminent. The magic number is easy to
remember—look for 80% of the battery’s
rated CCA value. (This is not an arbitrary
value; it is based on standards established by
the Institute of Electrical and Electronics
Engineers, IEEE.) At that point, it’s time to
replace the battery if you want to ensure its
continued reliability.Diagnostic Meter
Although clearly an automotive-based instru-
ment, a diagnostic meter is easily adapted to
marine uses and provides added functionality
and increased accuracy over a battery conduc-
tance tester. The Midtronics inTELLECT
EXP-1000, which costs about $1,100, has
functions for battery, starter circuit, and alter-
nator testing, as well as capabilities for voltage
drop testing. (As of this writing—2007—I
know of no other units with voltage drop test-
ing capability via conductance testing.) With
the inTELLECT EXP-1000, you can isolate
circuit faults caused by loose, corroded con-
nections or undersized wiring—two common
problems on boats—and it can also function
as a multimeter.
Features of the inTELLECT EXP include:- Comprehensive battery tests, with an
improved algorithm (compared to the
Micro500XL) for more accurate tests on
deep-cycle batteries as well as AGMs and
gel-cells. - Capability to create performance graphs
for such things as starter current draw and
alternator output. These features can be
extremely useful in analyzing marginal
performance situations.
At the end of the charging system test, the Micro500XL
provides an overall analysis of the charging system. In this
example, the system is normal.This screen displays the actual voltage for the loaded and
unloaded tests. As you can see, the voltage reading in the
unloaded test is higher (by 0.13 V) than the voltage at the
battery terminals with the engine turned off. This difference
just means the charging system is doing something. How-
ever, if the unloaded voltage is more than 2.5 V above
the initial battery reading with the engine off, then the volt-
age regulator is at fault. If the loaded voltage is less than
0.5 volt above the static battery voltage, the alternator’s
amperage capacity is too small for the loads it is serving.89