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What Is A DC To DC Charger And Why You Need One

This post was updated on March 15th, 2024

DC To DC charger infographic

How Does A DC To DC Charger Work?

A while back, I wrote an article entitled “Battery Not Charging? Here’s What To Do.” In the comment section, a reader asked me why I didn’t mention smart alternators and the need for a DC to DC charger. Until that time, in my 50+ years selling and servicing towable RVs, I had never heard of a DC to DC charger.

Thinking I was behind the times, I asked several of my RV dealer friends about smart alternators and how they could charge the house batteries on towable RVs. It seems I wasn’t the only one behind the times.

A little research concerning smart alternators and charging auxiliary batteries lead me to the REDARC website. There I quickly learned what a smart alternator is, why they aren’t effective in charging an auxiliary battery, and how to tell if my truck was equipped with a smart alternator.

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It turns out, to meet stricter mileage requirements, smart alternators produce the minimum power required to operate the primary vehicle, leaving little (if any) power remaining to charge an auxiliary battery. I have always thought the 12-volt charge coming from my current truck was lacking, as it never seemed to charge the house batteries in my travel trailer very much, even after a long day of traveling.

Following the instructions on the website, I determined I did not have a smart alternator. I did, however, discover my alternator wasn’t sending much power back to my house batteries. Additional research revealed a DC to DC charger could also be beneficial to those of us with “dumb” alternators too.

“If you plan to rely on your alternator significantly to charge your RV batteries, it’s definitely a good idea to have a DC-DC charger added to your RV electrical system.” Says RV blogger Lynne Fedorick.

It’s easiest to think of a DC to DC charger as a multistage battery charger, powered by your alternator, that provides the correct voltage to properly charge your house batteries. 

A DC to DC charger is not just beneficial for those towing RVs with trucks either. Motorhome owners can also benefit from installing a DC to DC charger. In addition to the reasons already given, a DC to DC charger can be especially important for motorhome owners if they are upgrading to lithium house batteries. Due to less internal resistance, lithium batteries can be charged and discharged much faster than conventional lead acid batteries.

A discharged lithium battery can require more amperage than your alternator can provide, leading to overloading your alternator. This is especially true when the house batteries are located in close proximity to the alternator, as you are likely to find in a motorhome.

Just like a DC to DC charger can increase the charge rate to charge your house batteries quicker, it can also reduce the charge rate to protect an alternator when too much power is required to charge lithium house batteries.

Here’s a video that further explains the benefits of installing a DC to DC charger on your RV:


We have charge controllers for solar panels, 3 & 4 stage converter/chargers to charge house batteries from shore power, and we have autoformers to modify the shore power coming into our RV. All these devices “condition” the incoming power, making it the most efficient for the job at hand. Doesn’t it make sense to use a DC to DC charger to regulate the incoming voltage from your alternator too?

After 50 years of charging house batteries the “old school” way while driving, this old dog learned something new. I have decided a DC to DC charger might be right for me and is worth further investigation.

After inquiries with different DC to DC charger manufacturers, the folks at REDARC agreed to send me a DC to DC charger to install, review, and test. In the next installment, I will cover do-it-yourself installation, impressions of the unit, and a look at the increased charge rate gained after installation.     

RVers looking for valuable how-to information have learned to go to the experts. Forums such as and blog sites like RV LIFE, Do It Yourself RV, and Camper Report provide all the information you need to enjoy your RV. You’ll also find brand-specific information on additional forums like Air Forums, Forest River Forums, and Jayco Owners Forum.

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