How does a Dual Battery System Work?

Don’t run the risk of losing power to your gear, and ensure your vehicle is always ready to start up with the installation of a 4WD dual battery system.

A dual battery system is a vehicle system that uses a secondary battery in addition to the vehicle’s main starter battery. This secondary battery is used as a power source to auxiliary equipment and accessories. In a dual battery system, both batteries function as two isolated systems. While your vehicle’s engine is running, your starter battery works with your alternator to power your vehicle and its electronics.

If you’re looking at getting into camping or overlanding, depending on what handy accessories you’d like to have, a dual battery system is a good way to go. You could ofcourse connect them to your main vehicle battery, but what if your accessories draw too much power and leave you stranded with a flat battery?

Do Battery Types Matter?

A vehicle cranking or starting battery is designed solely to start the engine, with reserve capacity to power a few ancillary functions when the engine is off. If you enjoy the comforts provided by 12 volt lighting, a car fridge, or personal electronics – you need the power of a second battery to ensure you won’t be left high and dry with a dead cranking battery. A dual battery system offers a quick and safe way to recharge your batteries, ensuring your starter battery isn’t drained flat from running your accessories.

A standard dual battery system consists of two batteries: a primary battery (your vehicle’s battery), a secondary battery, cabling to connect the batteries, and a battery isolator (this protects both batteries from being drained). In this system, the vehicle’s alternator will charge the primary battery; the charge will flow through the cabling and the battery isolator to the auxiliary battery.

It is recommended to use a deep cycle battery as your secondary battery because it is designed to be charged and discharged on a regular basis, and provides sustained power over longer periods of time. A starting battery is not designed to be frequently discharged and charged, and will reveal a shorter battery life than a deep cycle one.

Although standard dual battery systems will basically work, they have a big disadvantage. They typically can’t charge your secondary battery back up to full. For this reason, it is recommended to use a DC charger rather than a battery isolator. A DC charger draws power from your primary battery, increases the voltage, and automatically manages the current flowing to your auxiliary battery.

DC Chargers

A DC charger is a charger that supplies a constant DC or pulsed DC power to the battery that is being charged. DC chargers are particularly popular within the camping environment as they can boost the voltage going to the auxiliary battery, which means there is no voltage loss (unlike with the battery isolator).

Unlike a standard battery isolator, the DC charger can achieve a maximum run time and a maximum life expectancy from your auxiliary battery. A basic battery isolator can charge your secondary battery for approximately 60 – 70 percent whereas a DC charger can charge it to 100%. A fully charged secondary battery is key because it maximises the battery life and offers a maximum running time of your appliances in between charges.

Benefits to Consider

  • Allows your vehicle to power a fridge, radio, lights, inverters, and whatever else you need while you have the ignition off.
  • There is no need to worry about draining your starter battery and becoming stranded.
  • It increases power available if you need to use your winch.
  • Is able to charge your secondary battery with solar panels.
  • It provides peace of mind in case of primary battery failure.

Where can you Install a Second Battery?

A second battery can be installed under the bonnet if there’s space. A universal battery tray will work for some vehicles; while others may need a custom tray to suit their engine bay. If under-bonnet space is at a bit of a premium, there are ranges of battery boxes that provide a secure option for cargo areas or even utility tray installations.

How do you Charge the Second Battery?

There are a few ways to charge your second battery, the easiest is using the alternator from the engine to charge your second battery when traveling on the road. This can be easily done using a voltage sensing relay (VSR for short) or isolator switch. Solar is also another way to charge when the vehicle’s engine is not in use but as the voltage is very high, a solar to battery regulator is needed. The best of both worlds is a DC to DC Charger with a solar input. This is the more efficient way to regulate the input to your battery from both sources without damaging the battery over time.

These devices allow both batteries to charge while the vehicle is running and isolate the two when the engine is off. This will keep your cranking battery at full charge, while the second battery keeps your essentials cold – and the lights on.

Types of Auxiliary Batteries

Lead Deep Cycle
Suitable under the bonnet, or in an open tray or tub. Cheap, but are known to suffer from a reduced lifespan if not fully discharged and recharged each use.

AGM batteries are suitable anywhere as they do not let out any hazardous gases while charging. This type of battery is better suited to partial use and recharge, rather than fully discharging and recharging in a use cycle.

These boast reduced weight and increased capacity, lithium batteries are the most durable battery when used in a partial use cycle. However, due to heat restrictions these cannot be fitted under the bonnet of a vehicle.

You can rely on our experience

If a Dual Battery System for Auxiliary Charging is on your agenda for the many advantages to travellers either on or off the road, you can rely on Autospark to always be at the forefront of the latest innovations.

Autospark stocks a range of the most popular and best of brand versions to choose from like InterVolt, Redarc and Projecta and they are experts at fitting them for you too. If you need advice, you can always rely on the professionals at Autospark for the best in Auxiliary Charging.