Battery Selection

How do I select the right deep cycle battery for my application?

Proper battery selection may require the assistance of a knowledgeable battery sales/service
technician. Please contact Europower Battery Centre for assistance from one of our
Applications Engineers.

What is the difference between a deep cycle battery, a starting battery and a dualpurpose battery?

A deep cycle battery has the ability to be deeply discharged and charged many times during
its service life. It is designed specifically for powering electrical equipment for long periods of
time. An automotive or starting battery is designed for brief bursts of high current and cannot
withstand more than a few deep discharges before failure. This is why it is unable to start your
car if you accidentally leave the lights on more than a couple of times. For applications where
both engine starting and light deep cycling are required, a dual-purpose battery is often used.
This type of battery is neither a starting nor a deep cycle battery but rather a compromise
between the two so it performs both functions adequately.

Can I use a Deep Cycle battery as a starting battery?

Deep cycle batteries can be used for engine starting but starting batteries should not be used
for deep cycle applications. A deep cycle battery may have less cranking amps per pound than
a starting battery, but in most cases a deep cycle battery is still more than adequate for the
purpose of starting an engine.

What are the advantages and disadvantages of Gel, AGM and Flooded Lead Acid/Wet Deep Cycle batteries?

Generally, gel and AGM batteries have about 20% less capacity, cost about two times more,
and have a shorter cycle life than comparable flooded lead acid batteries. However, Gel and
AGM batteries do not need watering, are safer (no acid spilling out), can be placed in a variety
of positions, have a slower self-discharge characteristic, and are more efficient in charging and
discharging than flooded batteries (see table below). Gel batteries are more suitable for deep
cycling applications whereas AGM batteries are more for light cycling and engine-starting
applications.
trojanbatteryfaqtable1

What is better? 24 volt or 48 volt system?

Higher-voltage systems tend to be more efficient and put a lower load on the batteries. Factors
other than the battery enter into the system’s overall efficiency

Charging

How can a battery’s state of charge be accurately measured?

The state of charge of a lead acid battery is most accurately determined by measuring the
specific gravity of the electrolyte. This is done with a hydrometer. Battery voltage also
indicates the level of charge when measured in an open circuit condition. This should be done
with a voltmeter. For an accurate voltage reading, the battery should also be allowed to rest for
a period sufficient to let the voltage stabilise.

When do I need to perform an equalisation charge?

Equalising should be performed when a battery is first purchased (called a freshening charge)
and on a regular basis as needed. How often this might occur with your battery will vary
depending on your application. You will need to monitor your battery voltage and specific
gravity to determine when equalisation is needed. For example, it is time to equalise if the
measured specific gravity values are below manufacturer’s recommended values after
charging (recommended value for Trojan Deep Cycle batteries is 1.277 +/- .007 at 80o F).
Equalising is also required if the specific gravity value of any individual cell varies 30 points or
more. Reduced performance can also be an indicator that equalising is necessary.
Equalisation should also be performed when individual battery voltages in a battery pack
range greater than 0.15 volts for 6-volt batteries or 0.30 volts for 12-volt batteries.

Does my deep cycle battery develop a memory?

Lead acid batteries do not develop any type of memory. This means that you do not have to
deep discharge or completely discharge a battery before recharging it. For optimum life and
performance, we generally recommend a discharge of 20 to 50% of the battery’s rated
capacity even though the battery is capable of being cycled to 80%.

Do batteries self-discharge when not in use?

All batteries, regardless of their chemistry, self-discharge. The rate of self-discharge depends
on the type of battery, the age of the battery, and the storage temperature the batteries are
exposed to. As an estimate, Trojan batteries self-discharge approximately 4% per week at 80°F.

What type of charger should I buy?

An automatic charger offers the greatest convenience. Just plug the battery into the charger
and the charger does the rest. Manual chargers, although equally effective at charging
batteries, require a greater level of attention. Generally speaking, automatic chargers are
priced higher than manual chargers.

What size charger should I buy?

A properly sized charger takes into account battery capacity and the time interval between
charges. In applications where cycling is infrequent, such as weekend RV users, or infrequent
or seasonal trolling motor usage, a charger with an output current rating between 10 and 13%
of the battery’s rated 20-hour capacity will suffice. In applications where battery recharge must
be accomplished within 8 to 10 hours, a three stage, automatic charger, rated at 20% of the
battery capacity, may be required.

Example: A good charging rate for a battery with a 20-hr capacity of 225 amp hr is about 22 to
29 amps. You can of course go slightly higher or lower depending on what is available on the
market.

Maintenance

When should I water my batteries?

Water is lost during charging. Therefore, the best time to water your batteries is always at the
end of the charge cycle. However, if the electrolyte level is extremely low or the plates are
exposed to air, add some water to cover the plates before starting the charge cycle.

How often should I water my batteries?

How often you use your batteries will determine the frequency of watering. For example, the
weekend fisherman may find he only needs to water the batteries in his boat once a month.
While a maintenance supervisor for a golf course might need to service the batteries in their
golf cars every week. Also using batteries in a hot climate may require more frequent watering.
It is best to check your new batteries regularly as this will give you a good feel for how often
your application will require battery watering.

WARNING: A brand new battery may have a low electrolyte level. Charge the battery first and
then add water if needed. Adding water to a battery before charging may result in overflow of
the electrolyte.

What is the proper electrolyte level?

Liquid levels should be 1/8 inch below the bottom of the vent well (the plastic tube that extends
into the battery). The electrolyte level should not drop below the top of the plates.

Do you ever add acid to the battery?

Under normal operating conditions, you never need to add acid. Only distilled, deionised or
approved water should be added to achieve the recommended levels mentioned above. When
a battery is shipped in a dry state or accidental spillage occurs, electrolyte should be added to
the battery. Once filled, a battery should only need periodic water addition.

trojanbatteryfaqtable2

WARNING: Do not overtighten terminals. Doing so can result in post breakage, post
meltdown, and fire.

Can a battery freeze?

The only way that a battery can freeze is if it is left in a state of partial or complete discharged.
As the state of charge in a battery decreases, the electrolyte becomes more like water and the
freezing temperature increases. The freezing temperature of the electrolyte in a fully charged
battery is -92.0oF. At a 40% state of charge, electrolyte will freeze if the temperature reaches
approximately 16.0oF.

What is the specific gravity of a fully charged battery?

A hydrometer reading of 1.277 or greater indicates full charge for Trojan batteries. This value
is based upon a specified temperature of 77 to 80oF. For temperature correction values, see
the “Temperature” section of this FAQ. What are common mistakes made by lead acid battery
owners? Undercharging: Generally caused by not allowing the charger to restore the battery to
full state of charge after use. Continually operating the battery in a partial state of charge, or
storing the battery in a discharged state results in the formation of lead sulfate compounds on
the plates. This condition is known as sulfation. Both of these conditions reduce the battery’s
performance and may cause premature battery failure. Undercharging will also cause
stratification.

Overcharging: Continuous charging causes accelerated corrosion of the positive plates,
excessive water consumption, and in some cases, damaging temperatures within a lead acid
battery. Deep cycle batteries should be charged after each discharge of more than 50% of the
batteries rated capacity, and/or after prolonged storage of 30 days or more.

Under-watering: In deep cycle, lead acid batteries water is lost during the charging process. If
the electrolyte level drops below the tops of the plates, irreparable damage may occur. Water
levels should be checked and maintained routinely.

Over-watering: Excessive watering of a battery results in additional dilution of the electrolyte,
resulting in reduced battery performance. Additionally, watering the battery before charging
may result in electrolyte overflow and unnecessary additional maintenance. stratification.
Overcharging: Continuous charging causes accelerated corrosion of the positive plates,
excessive water consumption, and in some cases, damaging temperatures within a lead acid
battery. Deep cycle batteries should be charged after each discharge of more than 50% of the
batteries rated capacity, and/or after prolonged storage of 30 days or more.

Can I reduce my maintenance by not gassing my batteries?

You will reduce the frequency of watering, but will cause a condition known as stratification
where the specific gravity of the electrolyte is light at the top of the battery and heavy at the
bottom. This condition results in poor performance and reduced battery life.

How can I tell if a battery is bad?

To determine if the battery system is experiencing a problem, fully charge the batteries then
shut off the charger and remove all electrical loads. Allow each battery in the system to stand
on open-circuit for about one hour. Measure the voltage of each battery. If the battery voltage
spread exceeds .15 volts for a 6-volt battery, or .30 volts for a 12-volt battery, a problem is
indicated. Battery voltage alone does not confirm a problem. When the voltage spread
indicates a problem, confirmation is accomplished by taking electrolyte specific gravity
readings using a hydrometer. If the specific gravity readings show a spread greater than .030
(30 points), give the batteries an equalisation.

What is used to clean a battery and neutralise the electrolyte?

A solution of baking soda and water. Use 1 lb of baking soda for every gallon of water.

Temperature

How does temperature affect the performance of my batteries?

At higher temperatures (above 77oF) battery capacity generally increases, usually at the cost
of battery life. Higher temperatures also increase the self-discharge characteristic. Colder
temperatures (below 77oF) will lower battery capacity and prolong battery life. Cooler
temperatures will slow self-discharge. Therefore, operating batteries at temperatures at or
slightly below 77oF will optimise both performance and life.

How do I determine b battery capacity when it is colder or hotter?

Battery capacity is basically a linear relationship. A good rule of thumb is that for every 15oF
above 77oF, capacity is increased by 10% and for every 15oF below 77oF, capacity is reduced
by 10%.

How do I account for temperature when taking my gravity readings?

Temperature will affect specific gravity readings. As temperature increases, the electrolyte
solution expands and as temperature decreases the electrolyte solution contracts. As a
result, it is a good practice to temperature correct specific gravity readings. Here are the
relationships Trojan recommends using:
For every ten degrees above 80oF add 3 points to the hydrometer reading.

How do I account for temperature when taking my voltage readings?

Generally, gel and AGM batteries have about 20% less capacity, cost about two times more,
and have a shorter cycle life than comparable flooded lead acid batteries. However, Gel and
AGM batteries do not need watering, are safer (no acid spilling out), can be placed in a variety
of positions, have a slower self-discharge characteristic, and are more efficient in charging and
discharging than flooded batteries (see table below). Gel batteries are more suitable for deep
cycling applications whereas AGM batteries are more for light cycling and engine-starting
applications.
trojanbatteryfaqtable1

Is there a maximum temperature for charging my batteries?

Higher-voltage systems tend to be more efficient and put a lower load on the batteries. Factors
other than the battery enter into the system’s overall efficiency