Battery Selection, the Right Battery for the Job

battery selection, the right battery for the job

Consider the pros and cons of each model and the features and benefits they offer, when considering battery selection, the right battery for the job you want it to perform and the location where it will be fitted, is no different to weighing up the selection of the vehicle for the task it will be used for in the environment it will be operated. 

Battery options are clear cut as there is not the emotional side of decision-making regarding aesthetics such as whether the shape and colour are appealing. It is as simple asking what will the battery be powering and how long for, where will it be mounted and how will it be recharged?

The first step is to consider what the batteries role will be in your vehicle. The three commonly used terms referring to a batteries capabilities are Deep Cycle, Hybrid (or dual purpose), and Cranking. These three battery categories refer to the type of task that the battery is going to be performing. Deep cycle batteries are generally used for low power auxiliary loads where long run time is required, cranking batteries are used for high power short bursts like engine starting, and hybrid batteries are employed where it may be used for a mix of both.

A cranking battery is designed to deliver a large amount of current for a very short time. This shallow cycling of a battery is tolerated for around 30 seconds, where the voltage can be sustained at a useable level for the function of the starter motor and other vehicle electrical systems. This current level is called CCA (Cold Cranking Amps), generally rated at a very harsh -18c. To a certain point, the warmer the battery is, the more cranking amps can be achieved. For example, a battery that can deliver 800A at -18c may be able to deliver 1000A at 25c. This is one of the reasons that batteries fail to start the vehicle predominantly in cold conditions, after working at an acceptable level in warm conditions for quite some time.

In terms of state of charge, if this same 800CCA battery starts an engine that takes under 30 seconds to start and draws 800A when cranking, it will have only taken around 10% state of charge from the battery which is a safe level for a cranking battery. The time taken for the alternator to recover this charge in the battery is also quite short, though the alternator will only keep most cranking batteries around 70% – 80% state of charge in total.

The characteristics of the cranking battery make it ideal for starting the engine on vehicles, where the current delivery is high but only for a short period of time then recovered again. This cycle can be carried out many thousands of times in a battery’s service life as long as it is always in the top 10 – 30% of the battery’s state of charge. 

This is why it is recommended to periodically charge the start battery of a vehicle with a quality multi-stage charger such as the REDARC SmartCharge Battery Chargers. Charging with this method once a month will ensure your battery is in top health every time you turn the key.

battery selection, the right battery for the job

A deep cycle battery on the other hand is designed to deliver a small amount of current for a long period of time. The timeframe at which a deep cycle battery’s amp hours are derived is 20 hours at 25c. This means that dividing the amp hour rating of the battery by 20 will give you the number of amps it can continuously discharge for that period until flat when the battery is at 25c. For example, a 100Ah battery can deliver 5A for 20 hours before it is flat. Once again a colder battery, less than 25c, will have less capability at delivering power than a battery that is warmer than 25c. The interesting thing about deep cycle batteries is that if you discharge them substantially faster, you will achieve less amp hours from them, and if you discharge them slower you will extract more amp hours. This is known as Peukerts’ Law. For example the same 100Ah hour battery discharged at 50A will not last you 2 hours, you will more likely achieve around 1.5 hours before the battery voltage falls too low to run the device. Likewise the 100Ah battery may deliver around 120Ah if discharged at 2.5A before it is flat. Deep cycle batteries ideally should not be discharged below 50% or the number of cycles the battery can perform will be greatly reduced. If a deep cycle is discharged at excessively higher current than it is designed for, the number of cycles that it will achieve in its service life will also be reduced.

The ability of a deep cycle battery to deliver small current levels over long periods between recharging make them ideal for running auxiliary equipment such as lighting, radios, sleeper cab air-conditioners and fridges. The key to long service life here is to not over discharge the battery by having ample capacity for your usage, and charging them to 100% after each cycle. This can be achieved using an In-Vehicle Dual Battery Charger such as the REDARC BCDC. 

battery selection, the right battery for the job

A hybrid (or dual purpose) battery has properties which make it capable of delivering both high current for short periods and allow it to be deeply discharged safely to around the 50% state of charge. There is a small compromise however, where the cold cranking amps would not be as high as a pure cranking battery, nor would the amp hours be as high as a deep cycle – of the same case size and weight. These batteries are ideal for situations when the auxiliary battery will be used to assist the cranking battery when starting the vehicle, or to operate loads like winches, tailgate lifters, tarp winders, or any other load that draws a fairly high current but needs to run for an extended length of time between recharges. Hybrid batteries are also good if your system has a large inverter that will be powered by the auxiliary battery. Inverters can draw high currents when large loads such as kettles or microwaves are operated on them, but may only draw a small current when charging your phone or laptop from it. Once again, these auxiliary battery systems benefit from the use of an In-Vehicle Dual Battery Charger such as the REDARC BCDC.

So just like ensuring your vehicle has enough grunt to pull the load you need it to, reliably and for the long haul, it’s important to ensure that the battery you select is capable of delivering the required power to your electrical devices over and over again. 

For more information on how to take charge of your batteries visit www.redarc.com.au. 

battery selection, the right battery for the job