Advanced Marine Electrics and Electronics Troubleshooting A Manual for Boatowners and Marine Technicians

15

carbon pile load tester to determine the bat-
tery’s ability to supply amperage. Or if we didn’t
own a carbon pile load tester, we used a
voltmeter and checked the voltage across the
battery posts while cranking the engine or
running the anchor windlass.
These days, however, the vast majority of
boats have sealed batteries. These may be
either liquid electrolyte batteries or gel-cells
and absorbed glass mat (AGM) batteries
(referred to as immobilized electrolytebatteries
by the ABYC). Either way, a hydrometer is of
no use because there’s no cap to remove. And
while a voltmeter will safely determine the
battery’s state of charge, it won’t tell you any-
thing about the battery’s ability to deliver
amps. Neither will it tell you which cell is bad.
But that makes little difference because you
can’t replace individual cells. One bad cell
means you have to replace the battery.
Additionally, load tests on sealed batteries
are extremely dangerous. Although they are
referred to as sealed batteries, they are more
accurately termed sealed valve regulated(SVR)
batteries. This means that the battery can vent
itself if it develops excessive internal pressure—
for example, due to an overcharging condi-
tion. If this condition goes unchecked, the
electrolyte level will eventually fall below
the tops of the battery plates, which can cause
the battery plates to short-circuit. Conducting
a load test on a battery under these circum-
stances can produce an electrical arc inside the
battery case, which now has, as a result of the
overcharging, a hydrogen-rich atmosphere.
The result? Your battery explodes!
But even if you could use a battery load
tester, would you want to? The typical model
is heavy and cumbersome to get down into the
battery compartments on many boats. It’s so
much easier to use a handheld device.
Safety, value, functionality, and conve-
nience—all are sound reasons for using the

testing batteries, charging systems, and starter circuits

CONDUCTANCE AND IMPEDANCE

Conductanceis a measure of the ability of a battery to carry

current. It is the inverse of impedance, which is a battery’s

internal resistance. As a battery ages, its internal electrical

resistance increases due to sulfate coating on its plates and

general deterioration. The result is that impedance increases

and conductance decreases.

If you know your battery’s original specifications, you

can program them into a battery conductance tester to

determine the battery’s state of health.

new, alternative instruments and methods that

have been developed for battery testing.

Conductance Battery Tester

Several years ago, in preparation for an article

forProfessional Boatbuildermagazine, I re-

searched a new breed of conductance battery

testers. At the time, I was concerned about the

misconceptions and tales of woe I was hearing

regarding these instruments, yet I was also

intrigued by the possibility that they could be

more accurate than traditional battery testing

methods. I had only superficial experience

with them and had never looked at how they

worked. The research was eye opening. Since

then I’ve learned a lot about these devices and

have come to believe in their capabilities.

A conductance battery tester is easy and safe

to use. No load is placed on the battery, but

rather the tester sends low-level, pulsating volt-

age through the battery from the positive to

negative post. By timing this low-level signal,

the tester’s microprocessor determines the inter-

nal resistance, translates that into conductance,

and calculates the condition of the battery based

on the user-programmed specifications for the

battery. This is all accomplished in a matter of

seconds, and generally the battery does not