Safe Enclosed Trailer Auxiliary Battery Setup with Solar and No Backfeeding

Updated 05/07/2026 | Published 05/05/2026

Question:

Plan on getting enclosed trailer. Want to install a aux battery for interior lights and charger for charging 18v drill battery well out working. Lights wont stay on long just when moving equipment out and in. Ill have a small solar panel to keep it topped off when tailer is sitting also. Whats best and safest way so it doesnt back feed or drain truck battery or small trailer brake battery.

asked by: Damian

Expert Reply:

Hi Damian, I love this question.

The best and safest way to set this up is to run a completely separate auxiliary battery in the trailer for your lights and tool charging, and use a DC to DC charger Redarc # 331-BCDC1225D so you get proper charging with built in isolation and no risk of backfeeding into your truck or your trailer’s breakaway battery. That unit is a great fit for what you’re doing because it only allows charging when the truck is running, boosts voltage so your aux battery actually charges correctly, and it also has a built in solar controller so your panel can keep the battery topped off when the trailer is sitting.

You would simply run a charge line from your truck to the Redarc and then to your auxiliary battery, and this same unit will also connect to your solar panel and control that charging for you as well, so everything is handled in one place. Your lights and 18V charger would run off that aux battery, while your breakaway battery stays completely separate for safety. You also do not need to tie this into the 7 way at all, which actually helps avoid any unwanted draining.

I know the biggest concern here is making sure nothing backfeeds or drains something it shouldn’t, and this setup really takes that worry off your plate while keeping things simple and reliable.

What do you plan on hauling and charging most in the trailer, tools, mowers, or something else?

expert reply by: Heather A