What parts are there to dual-battery system?
 A
dual-battery system consists of the two batteries
with one termed as the ‘primary battery’ and the
other the ‘auxiliary battery’, battery cradles,
wiring for the discharging/charging system which
integrates the vehicle’s electrical system and a
battery isolator. An optional visual read-out
device can also be placed in the cab of the vehicle
for you to check on the battery charging or battery
power storage level.
Some larger 4WD vehicles come with two starter
batteries that are electronically paralleled for
starting the vehicle and this should not be confused
with a dual-battery system. Starter batteries can
have CCA (Cold Cranking Amps) marked on them.
Batteries and what is the best battery for a
dual-battery system?
There are two main types of batteries. When you
buy your vehicle from the manufacturer it will
likely have a ‘shallow cycle’ single high-current
discharge (HCD) battery. These HCD batteries or
cranking batteries provide a brief high amp charge
to start the engine.
Deep-cycle batteries are preferred as the
‘auxiliary’ battery for a dual-battery system as
they provide sustained power over long periods of
time and are designed for repeat charge and
discharge. These deep-cycle batteries can be larger
in size so the one you purchase will obviously need
to fit somewhere whether it is in the vehicle engine
bay or behind the seat in the vehicle cab.
Batteries come in various sizes and weights. The
number of internal lead plates can vary in number
ie: 7, 9, 13, 15, 17 & 19 and thickness so the amp
hour capacity also varies. Battery terminals can
also range from standard, standard/wingnut to dual
fit. Deep cell batteries also cost more.
There are wet cell and dry cell
batteries. Wet cell batteries give off hydrogen gas
which is an explosive vapour so you would not want
to place this type of battery behind the seat inside
a vehicle cab or near inverters, battery chargers or
any source of a likely spark. Care should be taken
when handling lead-acid batteries as any acid spill
can cause serious burns.
Flooded Batteries
These types of batteries also known as ‘wet cell’ as
the lead plates are suspended in wet acid and there
are caps on the battery for you to check the
electrolyte levels which require periodic topping
up. Wet cell batteries should be housed in a well
vented area and kept upright.
Gel-Cell Batteries
Gel-cell batteries are called ‘gel’ batteries as the
electrolyte is held in a jelly-like state and the
batteries are sealed and spill proof. A three stage
smart charger is required to charge these gel
electrolyte batteries. Gel-cell batteries hold
their charge longer than ‘wet cell’ batteries but
will suffer permanent damage if over charged. A
rest period will be necessary after rapid charging
to make sure the true state of charge is known.
Absorbed Glass Matt (AGM) batteries
so far have been considered to be the best or
superior for 4WD or RV use especially where the main
source of charge is from the vehicle’s alternator as
they are able to be recharged faster. AGM batteries
have a positive and negative plate separated by a
glass matt and the acid is also a gel. Reports
state AGM batteries are less sensitive to charge
rates than the gel-cell batteries. AGM batteries
are sealed, spill proof and maintenance-free.
Spiral batteries
Spiral batteries are a type of AGM battery with the
lead plates tightly compressed into spiral wound
cells. Spiral batteries are smaller in size,
lighter, sealed and maintenance-free. Spiral
batteries are reported to have a high cranking
performance, a longer shelf life (when not in use),
a higher charge acceptance rate during recharging
and more robust to withstand vibrations. Some
spiral batteries can be installed in any position
making for more flexible installation.
There is also a battery called Allrounder
which is built for starting and deep-cycle
requirements.
Good sturdy battery trays or battery
cradles are required to secure the battery in
the vehicle. Battery tray joins should be MIG
welded and those that are powdercoated will resist
abrasion and corrosion.
 Battery
life
will be extended if you do not run the battery down
more than 50% of their capacity. Deep cycle
batteries need a regular workout so it would be wise
to plug in the portable refrigerator every so often
to put the battery through its cycle.
It would also be a good idea to know how many hours
it will take for your vehicle’s alternator to charge
the auxiliary battery. A standard vehicle
alternator is not designed to recharge a deeply
discharged battery so it could take up to 5-6 hours
to charge an 85 Ah deep cycle. The vehicle’s
alternator can be modified with a specialised
charging alternator and a smart multi stage
regulator.
A few brand names for batteries are Century
Batteries, Trojan Batteries, Exide Endurance Deep
Cycle batteries, Optima Batteries, Federal Batteries
Deep Cycle Series and Concorde Lifeline AGM deep
cycle batteries.
Isolators and what they do
Battery isolators
do what the name suggests. They ‘isolate’ the
battery used to start the vehicle leaving it to
maintain its charge after you have turned off the
vehicle’s engine.
When you start a vehicle’s engine there is a surge
of power to the starter then the alternator starts
producing current. The isolator responds by firstly
providing power to the primary battery until it is
fully recharged then when the primary battery is
full the isolator switches the current over to
charge the auxiliary battery. 12V electrical items
are then run off the auxiliary battery.
Batteries can be isolated by a manual switch, a fuse
or an automatic switch. With manual switches to
turn the isolator on and off, human nature is that
you will forget to do so at one time or another. So
that leaves you with a battery management system or
automatic system. Automatic battery management
systems link batteries for charging and isolate
batteries for discharging.
To avoid any damage to a vehicle’s on board computer
or electronic fuel injection (EFI) system select an
isolator that has in built spike/surge protection.
The manufacturer of dual battery isolator Smart
Start, Redarc Electronics, recommend fuses be fitted
in the cable close to the positive terminals of each
battery for safety and to reduce the risk of fire.
Redarc website states:-
‘Fitting a fuse to one battery will protect that
battery but will not protect the other one and will
not prevent the fire risk. A fuse should also be
fitted in the line to the 12V equipment to protect
the auxiliary battery in the event of a short on
that line. Please note that if you are wiring the
vehicle with an emergency jump start switch via the
blue override wire from our Smart Start then the
fuses or circuit breakers must be suitably rated.
This is due to the high starting currents
experienced, which could result in blown fuses. In
this case battery starter cables must be installed
between the start battery and the auxiliary battery.
The same risks apply as described above therefore if
suitable fuses are not obtainable please ensure the
cables are well protected’.
Installation of a dual battery system
Installation of a dual battery system is best done
by an expert. It requires connecting into the
vehicle’s electrical system and this must take into
account the vehicle’s auto electrics. A certain
amount of frustration can also be experienced in
anchoring the sturdy battery cradle to accommodate
the weight of the deep cycle battery and finding
space for it in the vehicle engine bay. Care also
needs to be taken with the installation of the
isolator so it will not vibrate too much or melt
near exhaust heat. The type of wiring and cables
for a dual-battery system need careful consideration
to ensure a high charging rate to the auxiliary
battery and to avoid voltage drop.
Names of some of the products for dual-battery
systems and suppliers are, Redarc Electronics, ARRID
Advanced dual-battery controller, DBS Management
System, IBS Management System, Piranha Off Road
Products, TJM, ARB and eBay.
If you are technically minded dual battery
management kits are available from the above
suppliers and eBay.
For further information do a
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