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A Guide to Auxiliary Batteries

A Guide to Auxiliary Batteries

In choosing an auxiliary battery, the simplest answer to the question of ‘what battery should I get?’ is often how much are you willing to spend? We could spin various combinations when it comes to batteries but budget is usually the tipping point. With that being said, each battery type has its own merits with differences in sizes, weights, and chemistry that can influence which you end up choosing for your next dual battery setup.


Standard Lead Acid


A standard lead acid battery is the kindest on your wallet, with a 12v 100Ah deep cycle battery starting at approximately $350. Standard lead acid batteries are great all-rounder batteries, especially for someone setting up their first dual battery system. They are also very flexible batteries in terms of mounting location, as they are able to be mounted in the engine bay if there is no canopy room available.

The major downfall of standard lead acid batteries is the weight with a 100Ah battery starting at approximately 30kg. This adds a significant amount of weight to any touring setup and must be taken into consideration. They also require regular maintenance, needing to be topped up with electrolytes using distilled water.


dual batteries mounted in an engine bay

Some battery types can withstand the heat of the engine bay.




Coming in at the same price and weight point for a 100Ah battery as standard lead acid, the benefit of calcium batteries over standard lead acid is that they are sealed, meaning they’re maintenance-free. Similar to a standard lead acid, they can also be mounted in the engine bay and used as either a starting or deep cycle battery. 

Though calcium batteries do have some advantages over standard lead acid as they have an improved resistance to corrosion, no excessive gassing, less water usage, and lower self-discharge. They are also able to tolerate higher temperatures and environmental conditions, including vibration while driving.


Gel/AGM Batteries


As we move into Gel/AGM Batteries, we also start to move up in price, with a 100Ah gel battery starting at approximately $400. Though this isn’t much dearer than standard lead acid or calcium, it does pay to note that they cannot be mounted in an engine bay as the heat is too much and can be detrimental to battery life. This means that they can, however, handle deeper cycling without dramatically shortening their life. They’re also a similar weight to both calcium and standard lead acid, starting at about 30kg for 100 Ah.

Both AGM and Gel batteries have a similar reaction when charging which is why they share a charging profile on our battery chargers. Although like all batteries - besides lithium - it is not recommended to discharge below 50% to extend battery life. When deciding on a gel or AGM battery, because of the precise charging needed, you will need to purchase a charger with this specific charging profile.


dual battery charging off grid

REDARC's In-Vehicle Battery Chargers are designed to charge all battery types


Lead Crystal


The newest battery to the market, lead crystal batteries are another step up in price from AGM/Gel batteries, starting at approximately $600 for a 100Ah battery. Though this increased price is not unwarranted as lead crystal batteries require 30% of the total Amp Hour rating in charge current to achieve 100% state of charge. They can also recover from deep discharge better than other battery types as they’re able to accept higher charge currents.

Lead crystal batteries are built tough and because of this tend to be quite heavy, with a 100Ah battery starting at about 30kg. But this toughness means that they can withstand high heats and be mounted in the engine bay.


dual batteries

Having the right dual battery setup means you can stay off road for longer




The latest and greatest of auxiliary batteries, lithium (LiFePOâ‚„) is leading the charge when it comes to innovative battery features. At one third of the weight of other battery types, a 100Ah lithium battery starts at about 13kg. This makes lithium an easy choice for anyone who’s conscious of their rig’s weight. Although they are smaller than most battery types, they can maintain a higher output voltage during discharge cycles.

While other battery types are not recommended to discharge more than 50%, lithium batteries can handle up to 80% discharge meaning they have much more usable power than other battery types of the same amp hour rating. In addition to this, lithium batteries can handle a higher charge current, meaning they recharge quicker than other battery types.

The downside of this innovative technology is that it comes at a hefty price when compared to other battery types, starting at about $1500 for a quality 100Ah lithium battery. Another downfall of lithium is that because of their unique chemistry, you will need a charger with a specific lithium charging profile to ensure that they’re being recharged properly without damage. For more information on lithium batteries check out our blog post on the cost of lithium batteries.


choosing an auxiliary battery graphic


No matter which battery type you choose for your setup, it’s important to have a charger that will charge effectively without damaging this battery. REDARC’s range of In-Vehicle Battery Chargers are perfect for any setup, providing effective charging for all battery types – including gel/AGM and lithium.

For more information on designing and setting up a 12v system in your rig checkout Shaun Whale’s video on 12v setups.


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