Saturday, December 9, 2023


Smart DC to DC charging for RV lithium batteries

By Cheri Sicard
While recently undergoing an RV LiFePO4 lithium battery upgrade on my older travel trailer, I found some of the information about DC to DC charging confusing. Could I even charge my new LiTime 100Ah batteries while towing my travel trailer? As a complete RV lithium battery beginner, I didn’t know.

I should not have been surprised that Jared Gillis of All About RVs, one of my and our readers’ favorite RV YouTube hosts [239K subscribers, 30M views], already had a video about it.

What is DC to DC charging?

Jared says to think of this as a smart battery charger that uses a 12-volt source to charge the lithium batteries with multiple stages. That source can be your vehicle’s alternator or it can be a generator. This helps your batteries charge more effectively because it has both bulk absorption and float, depending on the type of batteries you use. So, yes, in addition to RV lithium batteries, a DC to DC charger will also work for lead acid and AGM batteries.

It can also charge the batteries in parallel with your RV’s solar system.

In a nutshell, a DC to DC charger will:

  • Charge your batteries more effectively as very little power gets through your 7-way plug while driving.
  • Lets you know how much DC power you can count on to charge your batteries.
  • Protects your vehicle’s alternator from potential damage that can occur when charging batteries if you inadvertently overload your alternator.

Be sure to watch the video because the charger you will use will depend on the size of the alternator.

Know that using your alternator to charge your batteries will reduce engine power and increase fuel consumption. Still, Jared says it’s not a bad trade-off and he gives tips on the video for how to optimize it.

Advantages of DC to DC charging your RV batteries

  • Even without solar it will give you a base of power to draw from.
  • With running their fridge off the inverter as they drive combined with their RV’s solar, Jared says they have plenty of power, plus they can add to their batteries charge, too.
  • It works as an effective isolator so that it disconnects when you turn your truck off and you don’t drain your battery.
  • It protects your alternator, especially with lithium batteries that have so low a resistance that they fry it. This is especially true on motorhomes where there is less space between the batteries and alternator.

Give the video a watch for more tips and wisdom on DC to DC battery charging.



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Neal Davis (@guest_257258)
1 month ago

Thank you, Cheri!

Drew (@guest_257162)
1 month ago

Don’t you camp enough for your converter to charge your batteries?

Tommy Molnar (@guest_257016)
1 month ago

Well, now I know what DC to DC charging is all about. The implementation seems way too complicated for me. With our 700 watts of solar on the trailer roof, lithium batteries, and appropriate solar controller, we just run our inverter to keep our 120v fridge going as we travel. Before swapping out our original RV fridge (which died a year ago), I used to use the electric side of the fridge the same way going down the road. So far, this has proved to be very effective and easy.

Cheri Sicard (@guest_257089)
1 month ago
Reply to  Tommy Molnar

I just had lithium batteries and a DC to DC charger put in (and battery monitor). So far it is working great.

Tommy Molnar (@guest_257158)
1 month ago
Reply to  Cheri Sicard

We installed a battery monitor when we went with the lithium batteries. For over 20 years I’ve wanted a way to follow the discharge rate as well as the charging rate. Now I can see when wifey plugs in her hair dryer, just exactly how much power that beast takes to work. Ha.

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