To understand why a deep cycle battery should be used in certain applications, we can compare a deep cycle battery with a standard car battery.
A car battery could be called a “shallow cycle”, providing a high burst of power for a short period of time, just long enough to start a car’s engine. Only a small portion of the battery’s power is used, and this is restored over time by the car’s alternator.
Standard car batteries have thinner lead grids and porous active material to maximise the surface area of the grid exposed to the acid.
Maximising the surface area provides greater current flow and as a result, greater starting power. However, because car batteries have thinner grids and more active material, they are not as reliable in providing long periods of power.
Unlike standard car batteries, deep cycle batteries are constructed with thicker grids of antimony lead alloy and a denser paste of active material to withstand discharge and recharge cycles.
This construction allows the deep cycle battery to deliver sustained power with low current drain for extended periods of time. Repeated cycling (discharge and recharge) does not cause the same level of damage that a car battery would sustain from the same process.
The ability to deliver steady power with long cycle life makes the deep cycle battery an ideal solution for a range of both recreational and industrial applications.
In recreational applications, deep cycle batteries may be found in golf buggies, caravans, scooters, four-wheel drive vehicles and boats.
Types of Deep Cycle Batteries:
There are several different types of deep cycle batteries available, each with specific features you will need to consider when determining the best battery for your application.
These are the most basic, widely used type of lead acid battery. Lead plates are suspended in wet acid which means electrolyte levels require periodic topping up. Flooded batteries are fairly tolerant of a range of charging rates and depths of discharge. However leaving flooded lead acid batteries to stand in a discharged state can cause irreparable damage.
The electrolyte of a GEL based battery is held in a jelly-like state usually within a sealed case.
GEL batteries can be left discharged for longer periods of time without affecting their ability to recover, however, the batteries require very strict monitoring of the charger voltage and a rest period is necessary after rapid charging to ensure the true charge state is known.
Absorbed Glass Mat (AGM) Batteries
AGM batteries consist of acid suspended in a special glass mat separator. This is state-of-the-art technology. AGM batteries have a higher charge acceptance rate than other types and they are not as susceptible as GEL batteries to damage caused by lack of charge voltage control. These batteries are sealed and do not leak if the battery case is fractured.
These are a variety of AGM batteries. Lead plates are in spiral configurations with acid saturated mat separators. They have a sealed case to eliminate acid spillage.
Some deep cycle batteries have a lead-calcium chemical composition, these batteries are said to be a little more tolerant to discharge and is encouraged by the usually cheaper price. Calcium batteries are often used in hybrid batteries where the battery can be used for deep cycle applications as well starting the car’s engine (high cranking amps). It needs to be considered that although these batteries can do both jobs, they generally wont last as long and often do not provide high Ah’s needed in some applications, therefore they may make a great Aux battery for a vehicle but not in a caravan or motor home setup. It is also worth noting that they require a high voltage charge up around 16 volts which many basic chargers can not provide neither does the cars alternator so it would need to be maintained on a multi-stage charger on a regular basis.
Dual Battery Systems
Many 4x4er’s, travellers, tourers and campers decide to install a dual battery system for the convenience and safety they provide. The deep cycle battery auxiliary battery will provide long-lasting power for recreational accessories. Such systems are common in boats, motor homes and 4WD’s.
A battery isolator controls the charging of batteries and separates them when the engine is turned off. This means you can get the most out of a deep cycle battery without running your starting battery flat.
Sizing the right battery
Deep cycle batteries come in a range of sizes to suit a range of applications. Whatever battery type you choose, it is important that you have adequate battery capacity (amp hours) to suit you applications and the requirements of your appliances.
The correct battery capacity can easily be calculated by establishing the total power consumption of your application, number of hours of usage and the operating voltage.
Now divide the total Watt Hours by voltage to obtain the required Amp Hours
Because vehicle power systems are not always perfect, we must always allow a little extra power in reserve by factoring in at least a 30% safety margin.
It is a much debated theory that batteries (no matter what type) should never be discharged to below 11.5 volts. Doing this is said to cause damage and lower the lifespan of the battery. It is also debated that you should never discharge your battery below 50% of its S.O.C (state of charge) therefore if your power requirement is approx 50Ah per day, than it would be recommended that you purchase a 90-100Ah battery. This of course is under the assumption you are able to fully recharge the battery at the end of the day. There are methods of recharging that can aid in assisting the battery to deliver its power such as solar power.
Getting The most From Your Battery
The life of a deep cycle battery is directly affected by the depth of each discharge cycle. A battery discharged with 70% remaining capacity will last much longer than one discharged to only 20% remaining capacity. The ideal compromise between initial cost, battery life and usefulness is to aim for approximately 50% discharge between recharges.
The single greatest cause of battery failure is when the battery is left in a discharged state for a prolonged period of time. If the battery is not recharged to full capacity quickly, it can lead to permanent loss of part of the battery’s capacity. This is particularly the case with flooded batteries. Also, leaving the battery in a discharged condition will also increase the likelihood of failure from a short-circuit.
Keeping your battery charged
When repeatedly using a deep cycle battery, it is important to ensure the battery is charged to full capacity after use. Not only does this mean your battery will be ready for use when you need it most, but you will also maximise the life of your battery.
The best type of charger to use is a multi stage charger. These chargers are controlled by a processor which reads the battery’s status and automatically determines the best charging conditions. These chargers usually have 3 basic stages, Boost, Absorption and Float. Boost will deliver maximum Amps to your battery to help stimulate a chemical reaction that is required to bring a battery to its full capacity. Absorption mode will slowly decrease the Amp output and increase the voltage depending on the type of battery that is connected. Float mode is basically when the battery is in full charge status and the battery is receiving a trickle type charge to maintain it ready for use. There are many multi-stage chargers available, some even 7-8 stage chargers which basically offer variances of the 3 basic stages. Some are smarter than others and can detect battery type such as AGM, GEL and Calcium and performs the correct conditions suitable for that battery type. All battery types require specific charging rates, it would be highly advisable to confirm with the retailer of your battery to ensure you have a suitable charger.
What do we use?
After nearly 3 years on the road, mostly relying on ONLY battery power for our fridge, lighting and vehicle operation we have changed ALL our batteries to CENTURY batteries after spending a fortune on other brands claiming to be suitable for rough roads and deep-cycle/quick charge applications. A lesson that I learnt is that buying cheap batteries to save money is simply feeding a FALSE ECONOMY- because you end up spending more in the long run as you have to replace the cheaper batteries more often.
In our vehicle we use a Marine Pro 720 battery as our starting battery. Although a “marine” battery it has ample CCA for starting our diesel engine on cold mornings plus it has a 100ah residual charge to allow for running a few accessories from it for a while. We use a 140amp battery isolator for our dual battery system and have another Marine Pro 720 as our AUX battery we use for our compressor fridge, LED lighting, power inverter, laptop power supply and whatever else needs running from the rear of our vehicle. Another benefit of the marine Pro 720′s are they can handle a bit of heat, a bit of bumpy road and actually like being cycled regularly so they don’t wear out easily!
In our Jayco Eagle camper we use a Century 120ah AGM battery. These are heavy but are safe for mounting inside the camper, have great tolerance to deep-cycle applications and are easy maintained by a generic battery charger.
A good tip when buying batteries, especially if you are thinking about travelling is to purchase them from a chain retailer. You can often take advantage of their bulk buying power for savings plus the keep your purchase recorded in the computer system so making a warranty claim is a lot easier. Plus there is a good chance of having an outlet in a close town no matter where you are. Another tip is to have the retailer do a load test on your new battery before you buy it- if its been sitting on a shelf for a long period of time, you want to know if it’s still good!
We recommend www.batteryworld.com.au as they have always given us great service and they have the right equipment to test your batteries for you. After all that all they do- is batteries!