PART 1: How to CONNECT a solar panel to a dual-battery system

Whether you’re a weekend camper or long-haul overlander, there’s no denying the convenience of a solar setup. Aside from having free energy to power your camping fridge, a solar panel can also be used to maintain your auxiliary battery for optimum service life.

With this in mind, here’s a basic guide on how to connect a solar panel to your dual-battery system or Portable Power Pack.


Simply put: A solar panel, a regulator, some heavy-gauge cabling, and of course, an auxiliary battery.

Although solar panels may vary in cost and quality, what’s just as important, is the regulator that goes with it. In short, the regulator is what converts the panel’s high voltage into a voltage that’s suitable for your battery; which means, the regulator must support your panel’s current and voltage rating.

Typically speaking, regulators are either MPPT or PWM in design. MPPT units are generally more costly, but noticeably more efficient in terms of how much energy they extract. PWM regulators may not be as efficient, but they are basic in function, reliable, and low cost.

It should also be noted that some panels have built in regulators, so be sure to check this before you purchase your panel.


If your vehicle is equipped with an on-board / installed dual-battery system, you simply connect the panel to the regulator, and the regulator to the terminals of your auxiliary battery.

On that note, it’s best to have your regulator as close to the battery as possible in order to limit voltage loss between the two. For this reason, it may be best to avoid panels with built-in regulators if you want the panel to be mobile and positioned away from your vehicle – resulting in a long cable and noticeable voltage loss.

What’s more, make sure you connect the regulator directly to the auxiliary battery, and not to your vehicle’s main / cranking battery.


As far as Portable Power Packs and Auxiliary Boxes are concerned, the installation is even easier: simply connect the solar panel to the regulator, and the regulator to the 50A grey coupler on your power pack.

On that note: National Luna recently launched a DC-DC Portable Power Pack, also known as the Green Box. This product is hugely versatile in that it features a 25A DC-DC dual-battery system, a built-in MPPT solar regulator, and a multitude of output power points.

The Green Box makes the installation of a solar panel super straight forward because the MPPT is already built into the unit. All you have to do is plug your solar panel directly into the Green Box’s solar input port, and the built-in DC-DC system takes care of the rest.

The National Luna Green Box is a portable power solution, that doubles as a dual-battery system, as well as a mobile solar setup. Best of all, you can use it in your vehicle, your campsite, or even in your house during load shedding.


Cabling is often the most overlooked subject when it comes to dual-battery systems and solar solutions. Ideally, we recommend nothing less than 16mm2 cabling between batteries, and 6mm2 from your solar panel to regulator.

How bad can voltage loss be? Depending on its diameter, a light-duty cable may double your auxiliary battery’s charging time, and in some cases, prevent the battery from fully recharging and fail as a result.

Next month, we’ll look at what size solar panel you need to run your camping fridge.

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