In today's world of overlanding and camping, the importance of batteries has grown exponentially. Gone are the days when camping had to mean disconnecting from all modern conveniences. Nowadays, powering items like fridges and lights has become part of our outdoor essentials, demanding reliable power sources to keep our adventures going smoothly.
Overview:
- Understanding The Different Battery Types
- Consider The Mounting Location
- Your Auxiliary Battery Depends On What You Will Be Powering
- Estimated Battery Run Times
UNDERSTANDING THE DIFFERENT BATTERY TYPES
The market offers a wide range of auxiliary battery types , including Gel, AGM, Flooded Lead Acid and the increasingly popular Lithium batteries. Each battery type has its advantages and disadvantages depending on the type of vehicle you own, how old the vehicle is, the desired mounting location and your budget.
CONSIDER THE MOUNTING LOCATION
The battery mounting location will play a big part when choosing a battery. For example, battery manufacturers will not warrant their batteries if mounted in high-temperature environments, like under the engine bay hood. It is highly recommended that only AGM/Lead Acid batteries be mounted in the engine bay.
For the inside of the vehicle, caravan, trailer, camper or similar, if not choosing the premium lithium battery path, then it would a Gel or AGM battery is recommended to meet the Caravan Standards and for safety.
AGM batteries tend to be more readily available and affordable compared to gel-type batteries. Both offer similar performance and maintenance requirements. AGM and Gel batteries are typically fully sealed, meaning they won’t don’t give off a sulphur-like smell when charging. AGM batteries also recharge faster than flooded lead-acid batteries.
The sulphur smell is associated with the battery’s gassing, and this chemical reaction that happens when the battery is being charged. This gaseous smell is a highly flammable hydrogen gas, and is not recommended for human health. That’s why sealed batteries are used for interior mounting locations, and it’s critical to follow the updated Caravan Standards for battery installation.
YOUR AUXILIARY BATTERY DEPENDS ON WHAT YOU WILL BE POWERING
Auxiliary batteries are used to preserve your main vehicle start battery for vehicle-specific duties such as starting the vehicle. Whilst your auxiliary battery is added to enable you to run your other recreational loads, such as a fridge, lights and inverters.
A quality choice for an auxiliary battery is a deep-cycle battery. This type of battery is designed for many discharges and recharges and can handle a lower discharge level.
However, be careful not to discharge an AGM/Lead Acid auxiliary Deep Cycle Battery/s below a level of 50% charge, as this type of continual over-discharging will reduce the performance and life expectancy of your Deep Cycle Battery. It is recommended to prevent your auxiliary battery voltage from dropping lower than 12 volts - 11.5 volts.
ESTIMATED BATTERY RUN TIMES
Whether you're travelling off-grid or going on a weekend trip away, understanding how long your battery will last is crucial. A simple way to prevent over-discharge and the risk of a flat battery is to add a dual battery system. However, to help understand how battery capacity differs by the chemistry of an auxiliary battery, below are a couple of examples of battery run times using estimated “round figures.”
POWERING A FRIDGE WITH A 100AH AGM AUXILIARY BATTERY
- 100 A/hr Lithium Battery
- Fridge in 35 Degrees Celsius ambient temperature
- Minimal opening and closing of the fridge
- Fridge draws 4 amps whilst running
- Due to higher ambient temperature and increased use, the compressor cycles on for 75% of the time
This means that in one hour, the fridge (only) consumes 1 amp-hour of charge from the battery. To avoid discharging the battery below 50%, there’s a maximum of 50A/hr of usable energy available from a fully charged 100A/hr AGM battery.
Under these conditions, we can run our fridge for almost 2 days without recharging the battery.
POWERING A FRIDGE WITH A 100AH LITHIUM AUXILIARY BATTERY
- 100 A/hr Lithium Battery
- Fridge in 35 degrees Celsius conditions
- Frequent fridge access (high usage scenario)
- Fridge draws 4 amps while running
- Due to higher ambient temperature and increased use, the compressor cycles on for 75% of the time
In this scenario, the fridge draws approximately 3Ah per hour from the battery (4 amps × 75% duty cycle).
A 100Ah lithium battery typically allows for deeper discharge, with up to 80% usable capacity. That gives us 80Ah of usable energy.
Based on this consumption rate, the fridge can run continuously for just over 26 hours, providing reliable performance for overnight stays or extended off-grid use.
The figures listed above are only examples, and the various loads, battery types, ambient temperatures, fridge temperatures, and frequency of use will affect this suggested power consumption and run time.
CHOOSE A HIGH-QUALITY LITHIUM AUXILIARY BATTERY FROM REDARC
Now that you understand the different types of auxiliary batteries, how mounting location and usage conditions affect performance, and what to expect from run times, you’re equipped to choose the right solution for your setup.
REDARC’s lithium auxiliary batteries are engineered for reliability, tested for the toughest Australian conditions, and designed to deliver consistent, high-performance power wherever your journey takes you.
REDARC's REDLAB Icon Battery range comes in 100A, 200A and 300A capacities and are built for life off the beaten path.
With IP67-rated rugged construction, ultra-high discharge capability, and seamless integration with REDARC charging systems, they deliver serious off-grid performance without the bulk. From corrugated desert roads to freezing alpine mornings, REDLAB batteries power through it all with 100% usable capacity, a built-in heater for below-zero charging, and advanced safety features certified to the latest standards. No matter where you roam or what you run, REDLAB gives you the confidence to go further and stay longer.
If you have any additional questions or need expert advice to select the right auxiliary battery for your setup, please do not hesitate to contact our dedicated team.
FREQUENTLY ASKED QUESTIONS
HOW TO CHOOSE A SECONDARY BATTERY?
Choosing a second battery depends on your power requirements, available space, and how you plan to use your setup. Consider your total power consumption, the type of appliances you’ll run, how long you’ll be off-grid, and whether you prefer low-maintenance options like lithium. Matching the battery to a compatible DC-DC charger is critical for long-term reliability.
ARE ALL AUXILIARY BATTERIES THE SAME?
Auxiliary batteries differ by chemistry (AGM, Gel, Flooded, Lithium), capacity, discharge rates, and temperature tolerance. Lithium batteries, for example, offer more usable power, lighter weight, and longer lifespans, whereas AGM batteries are more affordable and better suited for moderate use.
WHAT ARE THE DIFFERENT TYPES OF AUXILIARY BATTERIES?
There are many different types of auxiliary batteries, including:
- AGM batteries: sealed, maintenance-free and cost-effective.
- Gel: Similar to AGM but with more efficient deep discharge protection.
- Flooded lead acid: A traditional battery that requires maintenance.
- Lithium: High-quality, lightweight, high-performance, longer lifespan and up to 80-90% usable capacity.
