If you spend time off-grid, whether you're an overlander, camper, tradie, or weekend warrior, chances are you rely on 12V appliances like fridges, lights, and radios to make your adventures more comfortable.
But powering all that gear from your vehicle's start battery is a surefire way to drain the battery and be stuck with a vehicle that won't start.
That's where a dual battery system comes in. A dual battery setup lets you charge a secondary (auxiliary) battery while driving, so you can run your appliances without touching the power in your main starting battery.
In this guide, we'll discuss the pros and cons of a dual battery setup, what equipment you'll need, and what it costs to do it properly. Spoiler alert: Getting it right the first time is absolutely critical for overall cost-saving and high performance.
What is a dual battery system?
A dual battery system is a setup where your vehicle runs off the standard starter battery, and a second (auxiliary) battery is used to power external 12/24V appliances.
The two batteries are connected to allow your alternator to charge both, without the risk of draining your starter battery when you're off-grid or stationary.
This means your lights, fridge, radio, cooking gear, or any other equipment can keep running without leaving you stranded with a drained starter battery.
Read more: A guide on auxiliary batteries
Pros and cons of a dual battery system
Pros
- Power a range of appliances - 12V/24V fridges, LED lighting, radios, phone chargers, cooktops, and more.
- Keeps your start battery safe - never worry about being unable to start your vehicle after a night of camping.
- Extra power capacity - more stored power means more freedom.
- Solar integration - you can charge your auxiliary battery from solar panels.
- Backup power - if your starter battery fails, you may be able to use your auxiliary battery to get back on the road.
Cons
- Added weight - batteries and gear will add load to your vehicle.
- Installation complexity - a proper setup requires time, planning, and know-how
- Cost - good gear isn't cheap. Cheap gear can cause problems later.
- Maintenance and understanding - you need to monitor and maintain your system to keep it reliable.
What do you need for a dual battery system?
Setting up a dual battery system isn't just about tossing in another battery. You'll need a combination of components to work together safely and efficiently. Here's what we recommend:
1. Auxiliary battery
- Types: AGM, lithium, or lead-acid deep cycle.
- Deep cycle batteries are designed to handle long, slow discharges - perfect for running appliances.
Read more: Calculating battery size for your caravan or 4WD
2. DC-DC battery charger
- The DC-DC battery charger is necessary to charge your auxiliary battery from your starter battery.
Read more: DC-DC chargers
3. Battery isolator
- A battery isolator disconnects your start battery when the engine is turned off to prevent it from being drained.
- Allows charging of both batteries when the engine is running.
4. Battery monitor
- A battery monitor tracks voltage and state of charge levels, helping you monitor your battery health and usage.
5. AC Battery charger
- An AC battery charger is optional but helpful if you want to plug into mains power or solar to top up your auxiliary battery.
6. Ignition sense relay
- An ignition sense relay is required if your vehicle uses a smart alternator (common in newer models).
- Helps ensure your auxiliary battery still charges correctly.
7. Inverter
- An inverter is handy if you have appliances that use AC power like laptops, microwaves, or other household appliances.
8. Circuit protection
- Circuit protection includes fuses, breakers, and other components to protect your system from overloads or short circuits.
9. Wiring, cables, and fuses
- High-quality cabling and proper fuse placement are critical to prevent voltage drop or electrical fires.
How much does it cost to set up a dual battery system?
The cost of a dual battery system depends on the type of gear you choose and how complex your setup is. Entry-level kits might start around $800 - $1,000, but a high-quality, fully-featured setup with lithium batteries, solar integration, and monitoring gear can run $2,000 - $3,500+.
Be wary of budget kits under $500 - they often cut corners on wiring, isolators, or battery quality, which can lead to headaches (or worse) down the road. Spend once, spend right. Poor man pays twice!
We offer a range of kits tailored to different needs and vehicle types. Whether you want a basic weekend warrior setup or a fully off-grid touring rig, we've got options to suit.
Can you run two batteries off one alternator?
Yes! That's the core idea. The alternator charges both batteries while driving. A battery isolator ensures that once you stop the engine, your starter battery is protected from being drained.
Do you need an inverter for a dual battery setup?
Not always, but it's handy if you need AC power for things like laptops, kettles, or power tools (240V appliances).
What can I run off a dual battery?
Anything that matches your system's capacity. With the right battery and inverter, you can power:
- 12V/24V fridges
- Lighting systems
- Coffee machines
- Radios
- Microwaves
- Phone/laptop chargers
- Cooktops
- Power tools and more
What maintenance does a dual battery require?
Maintaining a dual battery system ensures it runs safely and efficiently, especially if you rely on it for camping, off-roading, or work. It's important to understand how your system actually works so that you are comfortable troubleshooting and performing quick repairs when required, rather than relying on a third party (who you may not be able to get hold of).
Here's a breakdown of key maintenance tasks:
1. Check battery voltage regularly
- Use a battery monitor or multimeter to check the voltage of your starter and auxiliary battery.
- A fully charged battery should read around:
- 12.85V for AGM or lead-acid.
- With lithium, you should always have a shunted battery monitor and check your state of charge, as voltage is not the best guide for a lithium battery.
- If the voltage drops below 12.0V frequently, it could indicate a problem.
2. Inspect connections and wiring
- Look for loose terminals, corroded connectors, or damaged cables.
- Keep terminals clean and make sure all connections are tight and secure.
3. Test the isolator or DC-DC charger
- Check that the isolator or DC-DC charger is working properly and is actually separating/charging the batteries as intended.
- When the engine is running, both batteries should charge. When the engine is off, the auxiliary battery should be isolated.
4. Maintain solar panels (if installed)
- Clean solar panels regularly for maximum efficiency.
- Check for damage or loose wiring in solar inputs to ensure proper charging.
5. Check battery health
- For AGM or lithium, use a battery monitor or Bluetooth app (if supported) to check battery capacity and charge/discharge rates.
6. Inspect circuit protection
- Make sure fuses and circuit breakers are intact and not showing signs of heat damage.
- Replace any blown fuses with ones of the correct amperage.
7. Use the system regularly
- Batteries that sit idle tend to degrade faster (due to sulfation - AGMs are prone to this)
- If you're not using the setup regularly, charge the auxiliary battery every few weeks to keep it healthy.
Wrapping up
A well-designed dual battery system is a game-changer for anyone who travels, camps, or works out of their vehicle. It adds flexibility, safety, and power to your setup - just make sure you choose quality gear, install it correctly, and know how to monitor and maintain your system.
If you're ready to upgrade or build your own dual battery setup, check out our range of kits and gear or get in touch with us for expert advice.
Springers Solar | Your Trusted 12V/24V Components & Accessories Supplier
We only stock the best brands in the extra-low voltage industry for the best prices - you can trust that when you buy gear from Springers, you are setting up your system to perform long-term. We don't waste our time or your time with low-quality products.
With an in-house team of 12V/24V experts, we can offer advice and support as you set up your off-grid, off-road, or DIY battery system. We are Queensland-based and house our stock, so check out our online store here or visit us at Lawnton or Capalaba for in-store help.
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What's Needed for a Dual Battery System?