Most commonly, batteries up to 200Ah require a DC-DC battery charger of around 25Ah. For ampere-hours exceeding 200, a 40-ampere DC-DC battery charger will work better.

If your alternator has a 200 amp rating, you’d want to take that number, and cut it in half and that would be the charged power. The reason it’s recommended to run it at 50% is that you never want your alternator to be running at its maximum output load because it’s really hard on the alternator and it wears them out.

To select the best size for your DC-DC charger, you should consider the following:

Alternator Size: Typically, alternators range between 60 to 150Ah while DC-DC chargers vary between 6 to 40Ah. You need to get a larger charger for optimal usage if you have a high-powered alternator with more capacity.

Battery Type: A DC-DC charger rated 20% of your battery’s amperage would work fine for conventional batteries such as AGM and lead-acid batteries. With a lithium battery, you can go higher, to almost 30% of your battery’s rated amperage.

Voltage: It is recommended to match your charger with your van’s electrical system. For example, if you have a 12-volt system (which is most common), you should go for a 12-volt DC-DC charger.

Usage: Your energy usage also plays a part in determining your DC-DC charger size. If you use several appliances with your auxiliary battery, you will need a DC-DC charger.

Popular DC-DC Charger Brands and their Cost

Now that you have an idea of how DC-DC battery chargers work, you may wonder which is the best brand to buy. To give you a heads up, several good brands are out there catering to different customer needs.

Here’s a brief overview of what this article discussed:

The DC-DC Battery Charger is the brain that tells your alternator how to properly charge your house batteries.

A DC-DC charger can maximize charging to 100% and optimize your auxiliary battery’s life.

Lithium batteries work well with DC-DC chargers as it efficiently manages the power input.

A DC-DC charger size depends on your usage, voltage, and battery life. As a general rule of thumb, a 200 Ah battery requires a 25 A DC-DC charger, while bigger batteries require a 40 A charger.

Recommendation: You should choose RedArc to buy the best DC-DC charger suited for your needs.