If you’ve ever camped off-grid, worked from your vehicle, or spent a day powering tools and gear away from mains power, you know how quickly energy runs out and draining your start battery is the last thing you want. That’s why so many people add an auxiliary battery to their setup.
An auxiliary battery, also called a secondary battery, is an extra battery installed in your vehicle, trailer, RV, or boat. While the starter battery is dedicated to cranking the engine, the auxiliary battery powers your accessories and equipment.
This separation ensures you can run appliances like:
- Portable fridges
- Lights
- Inverters
- Pumps
- Communication gear
- Power tools
With an auxiliary battery, your gear stays powered — and your starter battery stays ready to get you back on the road.
HOW DOES AN AUXILIARY BATTERY WORK?
The auxiliary battery is linked to your vehicle’s electrical system through a charger or isolator.
- While driving: The alternator charges both the starter and auxiliary batteries.
- When parked: The two batteries are isolated, so accessories only draw from the auxiliary battery, leaving the starter battery untouched.
This setup keeps your starter battery safe while still giving you reliable power for your accessories.
If fitted, solar panels can keep your secondary battery topped up whether you’re parked at camp or on the road.
WHY DO YOU NEED AN AUXILIARY BATTERY?
- Protect your starter battery - Avoid being stranded with a dead starter battery. The auxiliary battery powers your accessories, leaving the starter charged and ready.
- Power more gear - Run energy-hungry equipment, fridges, lights, inverters, or pumps, without worry, even when parked.
- Stay off-grid longer - Pair your auxiliary battery with solar panels and a DC to DC charger for days or weeks of power without plugging in.
- Safe, more reliable power - Modern lithium auxiliary batteries, like REDARC’s LiFePO₄ range, are lighter, more efficient, and longer-lasting than traditional lead-acid batteries.
WHERE ARE AUXILIARY BATTERIES USED?
Auxiliary batteries are valuable anywhere extra power is needed:
- Camping & Overlanding: Keep fridges, lights, and electronics powered off-grid.
- RVs & Travel Trailers: Run appliances and charge devices at camp.
- Boats & Marine: Support pumps, lights, and electronics without draining the starter.
- Work Vehicles: Power tools and equipment on the job without mains power.
WHY CHOOSE REDARC'S LITHIUM AUXILIARY BATTERIES?
Not all auxiliary batteries are created equal. REDARC’s lithium iron phosphate (LiFePO₄) batteries deliver higher performance, safety, and efficiency for serious off-grid and mobile setups.
Key Advantages:
- Lightweight & Compact: Up to 50% lighter than lead-acid batteries
- Long Life: 5,000+ cycles for years of service
- Fast Charging: Optimized with REDARC BCDC chargers
- Safe & Stable: Built-in Battery Management System (BMS) for overcharge, short-circuit, and temperature protection
- High Discharge Rates: Capable of running heavy loads and high-powered gear
Rugged, vibration-resistant, and built for real-world conditions, REDARC lithium auxiliary batteries are ideal for 4x4s, RVs, boats, and work vehicles.
Not sure which battery is right for your system? Read our guide on how to choose the right battery for your setup.
An auxiliary battery is the heart of any reliable off-grid or mobile power system. By separating starter and accessory power, it ensures you can run your gear without risking a flat starter battery.
With REDARC’s lithium auxiliary batteries, you get lighter weight, longer life, faster charging, and safer operation — making them the ultimate choice for anyone who relies on their power system.
To Learn more, explore REDARC’s lithium battery range or speak with a REDARC retailer to learn more.
