Battery Selection – Right Battery for the Job – Part 2

Battery Selection – Right Battery for the Job – Part 2

This is the second in a series of three articles by REDARC Electronics, Battery selection – right battery for the job – part 2.

Location location location! Where on the vehicle a battery will be fitted is a key consideration when determining which type of battery will be used. 


In part one we looked at the job of the battery and the factors that come into play regarding the battery selection to suit its purpose, now it’s time to consider the environment it will be operating in. The three battery types, Cranking, Deep Cycle, and Hybrid (or dual purpose) can all be sourced in different construction types to suit the spot on the vehicle that they will be fitted, the harshness of vibration they will be subjected to, and the temperature ranges they will operate in.

The five most common automotive battery construction types are referred to as Gel, AGM, Standard Lead Acid, Calcium and Lithium (LiFeP04). Here is a brief outline of these constructions:

Gel: A VRLA (valve regulated lead acid), or also known as sealed battery, that has the plates submerged in a jellified electrolyte. Being a VRLA they can be safely used in confined or poorly ventilated locations, and can be mounted in any orientation. The required charge voltage is typically 14.1V – 14.6V (per 12V battery). Gel batteries are generally not recommended for high temperature environments due to their low gassing point and valve pressure setting which if exceeded can be detrimental to battery life. They can however tolerate deeper cycling than other constructions without dramatically shortening their life. The electrolyte is not serviceable in Gel batteries.

AGM (absorbed glass mat): A VRLA battery that has the plates packed between fibre glass mats. These mats have the electrolyte absorbed into them. Being a VRLA they can be safely used in confined or poorly ventilated locations, and can be mounted in any orientation. The required charge voltage is typically 14.1V – 14.6V (per 12V battery). AGM batteries are generally not recommended for high temperature environments due to their low gassing point and valve pressure setting which if exceeded can be detrimental to battery life, though some are an exception to this rule due to the high internal pressure they can tolerate allowing greater gas recombination. Spiral or cylindrical cell AGM batteries of certain brands can tolerate higher temperatures than other AGMs due to this. The electrolyte is not serviceable in AGM batteries.

Standard Lead Acid: Also known as flooded batteries, the electrolyte is a free-flowing fluid in which the plates are submerged. The electrolyte in these batteries can be topped up which makes them ideal for use in higher temperature environments where evaporated electrolyte can be replenished with demineralised water. This also makes them unsuitable for confined or poorly ventilated locations as the hydrogen gas vented during charging is corrosive and flammable. The required charge voltage is typically 14.4V – 14.9V (per 12V battery). These batteries are generally cheaper to manufacture and therefore cheaper to purchase than the other construction types.

Calcium Content: A flooded battery with calcium content in the plates, commonly VRLA. The calcium content reduces gassing while charging which decreases electrolyte evaporation, and also resists corrosion of the plates which helps extend the batteries service life. Calcium content batteries have the highest voltage requirement for charging typically 14.8V – 15.3V (per 12V battery). Due to the reduced gassing these batteries are ideal for higher temperature and environment and also have generally good vibration tolerance.

Lithium: (LiFeP04) batteries are constructed using individual cells that are managed by internal BMS (Battery Management System), housed in a polycarbonate case. The BMS ensures cells are balanced and they do not overcharge or discharge. These batteries are maintenance free and do not vent gasses making them suitable for installation in different orientations and enclosed areas. When charging LiFeP04 batteries it is recommended to use a charger with a lithium charge profile with a charge voltage of around 14.5V. A couple of key benefits to using lithium batteries are the reduced weight (11.9kg per 100Ah), flat discharge curve, increased cycle life and charge efficiency. Some lithium batteries can be installed in engine bays, but it is recommended checking with the manufacturer.

Please note that the figures here refer to the battery types generally, and the battery manufacturer data sheet for the specific battery in use should be consulted for information relating to items such as required charge voltage.

So given the characteristics of each of these five battery types, it can be seen straight away that some types are better suited to certain locations and environments. As AGM batteries have their plates in a supporting material, compressed between the fibre glass mats, they are generally a strong construction, tolerant to vibrations on rough roads or tracks. Standard and calcium batteries can be made to tolerate these harsh conditions when constructed with stronger plates and extra support within the casing, these stronger units are sometimes referred to as marine, four wheel drive, or commercial/industrial batteries.

Battery Selection – Right Battery for the Job – Part 2

The most common location the vehicle starting battery is fitted is close to the engine bay. The important characteristics here are strength, heat tolerance and ability to deliver sufficient cranking amps reliably to the starter motor. So standard lead acid or calcium batteries are a must for engine starting batteries, or even certain brands of AGM.

When it comes to auxiliary batteries, the installation locations vary greatly. If the battery is on the vehicle chassis, it could be close to the engine bay, in the cab underbody or way down the back of the vehicle on the chassis. The auxiliary battery may be mounted on a trailer, such as in a tool box or on the chassis itself. Commonly prime movers have them mounted behind the cab on the chassis, and rigid vehicles have them on the outside of the chassis rails.

Auxiliary battery installations close to the engine bay call for the same characteristics of a standard, calcium or some AGM batteries in terms of strength and heat tolerance, as the start battery does. The difference is that if the battery is to be used as a starter backup or to run a large inverter, as well as being capable of deep cycling for running a fridge and sleeper cab air-conditioner or alike, then a hybrid battery should be used. If the battery is going to be for a fridge and sleeper cab air-conditioner only, then a pure deep cycle should be used to maximise the available amp hours in the space available. In saying that, if your start battery fails or is flat and you are really stuck, you would choose to sacrifice some service life of the deep cycle and use it to assist the start battery in this situation regardless.

Auxiliary batteries that are to be installed inside the vehicle cabin, an enclosed body, enclosed tool box or boot, must be a sealed VRLA or lithium battery. The hydrogen gas emitted from non-sealed batteries will corrode metals around the fitting location, and pose a potential explosion risk should the gas build up and a spark or flame occurs. The VRLA battery range in AGM, Gel, calcium and lithium leave plenty of options regarding case dimensions and price. 

If the vehicle is purely for smooth city road use then a Gel battery that can withstand harsh deep cycling would be a great choice. If the battery needs to be fitted in a position other than upright, an AGM or lithium would be the way to go, additionally, these batteries will not lose their electrolyte immediately if the case is damaged unlike flooded cell Calcium and standard batteries. 

An off-road or long haul vehicle or trailer would benefit from an AGM or commercial/industrial Calcium battery for longer life over the long distances of relentless vibration. If the auxiliary battery is to be used for those low current loads providing a long runtime between recharges, then a pure deep cycle is required. However if a large inverter is also to be run from the battery then a hybrid is a good choice to also help deliver the larger currents when needed.

Making sure you have the right battery for the location it is installed in will help maximise the effectiveness and service life of the battery, adding up to it being better value for money in the long run. No matter what battery you install, it needs to be charged correctly. 

In part three and the final segment in our battery series we will look at providing the right charge to the battery.

To ensure you get the expected performance and value for money from your batteries, make sure you refer to the battery manufacturers’ data sheet and visit to select your battery charging solution.