Do you take a mobile fridge/freezer with you on your travels? Or have so many gadgets plugged into your vehicle that it drains the battery? Yes, a dual battery system offers a solution – but there are a few things you need to consider.
Adual battery system consists of a second (or third) battery that’s connected to your vehicle’s alternator. The purpose of the auxiliary battery is to provide electricity to your fridge or coffee machine without draining your main battery. You can devise your own dual battery system, or you can buy one of the many existing systems and have it installed in your vehicle.
How to install it
The simplest way is as follows: Connect the end of one battery lead to the negative terminal of your main battery and the other end to the negative terminal of your auxiliary battery. Connect a second battery lead to the positive terminal of the main battery and the other end to an isolator. From the isolator there’s another battery lead that runs to the positive terminal of your auxiliary battery. Remember that you need to add fuses to the positive battery leads in front of and behind the isolator. Now you’re ready to connect your favourite camping device to the auxiliary battery. The reason you need an isolator is so that your fridge/ freezer won’t drain the main battery’s power. The isolator can be a simple switch you flip on and off yourself, to charge the auxiliary battery. It is a hassle, however, because before heading off in the morning you first have to drive for a few minutes to charge your main battery back up to 12,6 V; then you have to pull over to flip the switch, so the auxiliary battery also charges; and when you arrive at your destination, you have to flip the switch again to isolate the main battery so it’s strong enough to start your vehicle’s engine tomorrow morning. Sounds like a mission. So to get the most out of a dual battery system, we suggest an intelligent solenoid. This device automatically detects when your
main battery is fully charged, and only then will it share the electric current generated by the alternator with your auxiliary battery. If you want to mount the auxiliary battery in your caravan or off-road trailer, you can’t use the standard light connector to charge the battery. It’s not robust enough to handle a charge current, and will probably melt. Rather get 12 V, 120 Ampère Anderson connectors to connect the battery leads between your towing vehicle and your trailer. The installation of a dual battery system is something best left to a qualified auto electrician, but if you like to DIY you should consider getting a National Luna dual battery system. It’s super-easy to install yourself, and it delivers excellent results. We chatted to Peter Slement, owner of National Luna, about their do-it-yourself system.
Asked and answered
Where should the auxiliary battery be fitted? “Underneath the bonnet is a good spot if you want to mount the system permanently, but National Luna offers a portable dual battery system that you put in the back of your SUV and take out at night if you want to use it in your tent.” Isn’t it risky to have a battery inside an enclosed space? “Look, if you can smell the sulphuric acid and hydrogen in a battery, it’s definitely time to replace it. In any case, you should stay away from the old type of battery, with plugs that constantly need to be refilled with battery water. A modern, sealed battery won’t emit toxic gases in your vehicle.” What kind of battery is the best? “The simple answer is that the auxiliary battery should be as big as possible (maximum Ampère hours), because you never want it to become completely flat. At National Luna we prefer the absorbent glass mat (AGM) battery, because it recharges quickly, operates like a deep cycle battery, and releases a high load.” Is an alternator strong enough to charge all these batteries? “Your motor’s alternator is not a deep cycle charger. You’ll eventually realise that the auxiliary battery always draws the shortest end of the stick and will often not be fully charged, especially if you switch your vehicle’s engine off often or drive short distances. Besides that, you’ll probably have to upgrade your vehicle’s standard alternator; it’s also essential to regularly connect your auxiliary battery to a smart charger that measures the condition of your battery, and recharges it with the correct current and voltage.”
The purpose of the auxiliary battery is to provide electricity to your fridge or coffee machine without draining your main battery.