system aboard a vessel provides the power for most of the onboard
systems, including: lighting, bilge pumps, fresh water and waste
water pumps, a wide array of navigation systems, anchor winch,
entertainment systems and the engine starting system. An understanding
of their selection, care and maintenance will protect your investment.
Regular maintenance will also greatly improve their operational
|Modern boats have sophisticated electronic navigation systems
installed, requiring a steady supply of power.
Batteries can be divided into several different
types, these include: lead acid batteries; gel batteries (commonly
called recycling batteries), and nickel cadmium or Nife batteries.
Lead acid batteries
These are by far the most common type of batteries
used aboard boats today. Lead acid batteries contain lead plates
with separators to differentiate the positive plates from the negative
plates. The electrolyte is made up of 35 percent sulphuric acid
and 65 percent pure water.
Many people use truck batteries aboard their boats.
These batteries are generally not well suited to the marine environment
because truck batteries are designed for constant use, while marine
batteries are designed to survive less frequent use. Truck batteries
will self-discharge at the rate of approximately two percent per
week while marine batteries will self-discharge at the rate of
approximately 0.5 percent per day. However truck batteries can
last well aboard boats that are in constant use, such as charter
vessels and fishing vessels.
Lead acid batteries are by far the most commonly
used batteries today. They can be divided into two categories.
These are deep cycle batteries and engine starting batteries.
Deep cycle batteries
These batteries are designed for continuous heavy
use and are more robust in their construction than starting batteries.
This ensures a quick recovery during use. Typically these batteries
will sustain 700 deep cycles and approximately 7000 shallow cycles
before the battery fails. The lead plates are approximately four
millimetres thick and the separators are made of glass fibre with
a mat backing to encapsulate the positive plate as it expands and
contracts during the cycling process. The grid metal has twice
the antimony content when compared to starting batteries.
Water loss is a marked characteristic of these batteries;
thus the water level should be checked regularly. Deep cycle batteries
do not recover well if subjected to water loss for a sustained
period of time.
|A hydrometer will give a more accurate reading than a voltage
Engine starting batteries
These batteries are designed to provide high amperes
output for a very short period of time. A typical scenario when
starting an engine. The lead plates are approximately 1.5mm thick.
These batteries do not lose water as rapidly as the deep cycle
batteries. If starting batteries are subject to deep cycling, their
performance will typically deteriorate rapidly.
Maintaining long battery life:
Water loss does irrevocable damage to a battery, especially if
the water loss is sustained over a prolonged period. Batteries
should only be filled with distilled ion-free water up to the
bottom of the filler tubes. If the battery is over-filled the
risk of spillage is increased. The water in a battery also
acts as a cooling agent; this is another reason why it is important
to maintain the correct water level at all times. If battery
plates are exposed while under heavy load or while being charged,
they can glow red hot. If this is ever encountered the operation
should be stopped immediately and the area evacuated, as there
is the serious risk of a violent explosion.
The outside case of the batteries should be kept
spotlessly clean, especially around the posts. This is to ensure
an electrical short is not created that can quickly flatten the
battery or reduce its performance.
|These batteries are tightly constrained and not able to move,
even at large angles of heel. Note the isolation switches inside
the battery box. This is not a good idea.
Lead acid batteries should be fully charged every
three weeks in the wintertime and every fortnight during the summer
to maintain optimal performance and lifespan. If a battery is left
in a discharged state it will quickly start to grow lead sulphate
crystals on the plates. This insulates the plates from the electrolyte
and seriously hinders recharging. If the lead sulphate crystals
are left to grow for sufficient time the battery cannot be recharged
and thus becomes useless. The lead sulphate is easily identified
as a white film on the lead plates. The warmer the temperature,
the quicker the crystals will grow. For every five degrees (Celsius)
increase in temperature, the growth of the sulphate crystals is
Batteries should never be charged with excess volts
as this does permanent damage. The usual charging voltage for a
12 volt battery is 14.2 to 14.4 volts. Excess voltage during charging
also promotes gassing and water loss. When a battery is being charged
it should not gas (produce bubbles in the cells). If this occurs
it indicates a problem with the battery cell and it should be investigated.
No two cells in a battery behave exactly the same.
Especially after the battery has been subject to heavy discharge.
Thus it is a good idea to keep batteries in good condition to ensure
Testing the charge of a lead acid battery:
The charge of a lead acid battery is commonly tested using a hydrometer.
A quality hydrometer can be obtained from any large hardware store
for approximately $25.
Table 1 is an approximate guide for the
state of charge (at 26.7°C):
Specific gravity is the measure of a liquid when compared to fresh
water at 15 degrees Celsius, which equals 1.0. When the battery
is at full charge the electrolyte in the battery is 26 percent
heavier than fresh water, (SG = 1.260). Note the specific gravity
of the electrolyte will change with the ambient temperature, but
for temperate climates this can largely be ignored.
Using a voltage meter does not always provide a
reliable reading, as they are influenced by the recent battery
cycles. When a battery has just been charged, the charge remains
on the surface of the battery plates for several hours, this will
give you a false high reading. Conversely any recent heavy load
on the battery will lower the charge of the battery for several
hours also giving a false reading. The hydrometer will provide
a more reliable reading, however it is affected by phenomenon known
as gravity bounce and stratification.
Gravity bounce occurs as the battery is being charged. The heavier
and more charged electrolyte sinks to the bottom of the battery
case. The sample of electrolyte that is drawn into the hydrometer
is from the top of the battery. Thus, it is not as dense or as
charged as the electrolyte at the bottom of the battery. As the
charging process progresses, the gasses that are trapped between
the plates and the separators escape and mix the layers within
the electrolyte, this gives rise to the characteristic sudden
rise in charge of the battery cell. Convection currents generated
by charging and heavy discharging also assist to reduce the
gravity bounce phenomena.
|Batteries should never be left on the concrete,
as they will rapidly discharge. Put a piece of wood under them
to prevent current leakage.
Stratification is similar to gravity bounce in that the specific
gravity of the electrolyte varies with the depth of the electrolyte.
However, where gravity bounce occurs during charging, stratification
occurs when the battery is left to sit perfectly still for a
period of time. This allows the heavier electrolyte to sink
and form a layer at the bottom of the battery. Stratification
can cause the voltage regulator to indicate that the battery
is fully charged. This is one of the reasons why some voltage
regulators have a periodic equalising charge mode, to stir
the electrolyte by causing the cells to gas for a short period
of time to stir the electrolyte and break up the layers.
Quick battery cell test:
A quick method of testing the condition of each cell in a battery
is to first open each battery cell cap. Then turn the engine
over, with the engine stop engaged and carefully look inside
each cell. A cell that bubbles indicates it has begun to break
down. The bubbling looks much like lemonade. The battery may
still produce power. However, if you test it you will find
the voltage and/or amperage has dropped. The battery should be
replaced. The damaged cell is producing a high rate of discharge
and this is why it bubbles. When looking into a battery cell
it is always wise to wear eye and face protection.
Gel batteries are commonly called recycle batteries.
These batteries are completely sealed and contain no antimony in
the battery. The plates are separated by a glass fibre mat and
have no liquid in the cells. As there is no liquid, these batteries
do not suffer from the problems associated with gassing. Gel batteries
are compulsory for all Category One racing yachts, to prevent the
spillage of acid in the event of a capsize.
Gel batteries are more expensive to purchase than
lead acid batteries. They have a life span of about six to seven
years, which is similar to that of a lead acid battery. Gel batteries
designed for deep cycle provide excellent service.
|This earthing block has been painted with
anti-fouling and is no longer usable. Earthing blocks are essential
to ensure the correct operation and minimal power-drain of
some shipboard electronics.
Nickel cadmium batteries
Nickel cadmium batteries are also called Nife batteries.
The electrolyte in these batteries is an alkaline mixture. Although
these batteries are expensive to purchase, they provide excellent
service and typically last from 12 to 15 years in marine applications.
These batteries are frequently used in heavy applications and where
maintenance requirements must be minimal.
Batteries should be securely fastened into a strongly constructed
acid-proof box with a strong lid attached. The box should have
a vent near the top to allow the ventilation of hydrogen gas
to outside of the vessel. The battery box should be placed
well above the bilge, in a position where it is subject to
|Two banks of batteries are utilised
here to drive the electric engine that has been installed in
a small powerboat.
Excessive vibration will eventually break down the
internal construction of a battery, rendering it useless. Where
practical, the battery box should also be placed well away from
sources of heat to ensure optimal battery performance. Ideally,
batteries should be above the level of the engine starter motor.
This allows the batteries to continue to operate essential safety
equipment such as a marine radio, should the engine become submerged.
The cables from the battery to the common power
bar should be the same size as the engine starter cables. Table
2 features a guide to the correct size.
Two cables of the same cross-sectional area can
be run in parallel if a single cable of sufficient size is not
available. It is imperative that the cables for the positive and
negative leads be of the same cross-sectional area.
Solar panels and
Solar panels and wind generators provide a good
way of keeping the batteries charged while the yacht is not in
use. However, it is important to ensure a voltage regulator is
fitted in the charging circuit. This is to ensure the batteries
are protected from over-charging. A unidirectional device should
also be fitted, so the batteries do not discharge through the solar
panel or wind generator when they are not providing a charge to
the batteries. The unidirectional device can be as simple as a
diode. But I would always recommend consultation with a specialist.
Care of battery posts:
The seal between the lead posts and the top of the
battery relies on the adhesion between the two disparate materials.
This seal is weak. Due care should be taken when connecting or
disconnecting the battery terminals. Methods such as hammering
the terminal, levering the terminal off and excessive tightening
or loosening without sufficient support should be avoided. When
this seal has been broken, acid will tend to work its way up the
battery post and start to corrode the terminal. Once the seal has
been broken there is no effective way of repairing it.
To ensure efficient battery connections, the terminals
should be soldered to the heavy battery cables and covered with
a plastic shrink wrap to prevent corrosion. The bare metal terminals
should be covered with Vaseline or light-grade grease to prevent
the build up of corrosion.
Batteries can be joined together in two different
ways – in
series or in parallel. Batteries connected in series are connected
positive to negative; this increases the voltage of the battery
bank. Batteries connected in parallel are connected positive to
positive and negative to negative. This increases the amperage
of the battery bank.
More than one battery bank can be connected together
to increase both amperage and voltage. See diagram below.
Some simple battery maintenance will keep your batteries working
at optimal levels.
Maintenance can be divided in
two categories, regular checks and annual tasks.
Regular battery checks are mandatory if the operation and life
of the battery are to be maintained. Regular checks include:
• Keep the battery case clean.
• Regular checks of the electrolyte level. Always use ion-free
distilled water to top up the level of each cell.
• Use a hydrometer to check the state of the battery charge
for each battery cell.
• Ensure the battery terminals are free of any corrosion.
• Ensure the bare metal terminals are covered with Vaseline
or light-grade grease to prevent corrosion.
Annual checks should be carried out during the winter
maintenance period. These include:
• Ensuring the battery tie-downs are in good order and have
not been damaged by spilt electrolyte.
• Remove the batteries from their box and clean the inside
of the box.
• Ensure the vent at the top of the battery box is clear.