Charge a Trailer Battery to be Able to Charge and Run a Winch

Updated 08/12/2025 | Published 08/06/2025

Products Featured in This Question

Deka Jacketed 2 Wire, 10 Gauge, Brake Wire - per Foot

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etrailer Trailer Wiring 7-Way Upgrade Kit w/ Junction Box and RV Style Connector

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Battery to Fuse Holder Cable for Redarc MIDI Fuse Kit

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23-Amp MIDI Fuse Kit for Redarc In-Vehicle 12-Amp BCDC Battery Charger

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$65.00

30-Amp MIDI Fuse Kit for Redarc In-Vehicle 12-Amp BCDC Battery Charger

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Redarc In-Vehicle BCDC Trailer Battery Charger - Single Input - DC to DC - 12V/24V - 12 Amp

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Question:

Rewiring my car hauling trailer. Plan to add 600-700 cranking 12 V for electric winch. What type/size of battery isolator/charger can I wire in to charge the battery from the tow vehicle, if I use the power supply wire from a 7 wire plug/connection configuration? Also may do away with small emergency break away batter and hook up to the big 12 v battery as well?

asked by: Mark

Expert Reply:

Thanks for your question, Mark!

Just want to make sure I’m understanding your setup correctly; you’re adding a battery to your trailer to power an electric winch, and you’d like to be able to keep that battery charged while towing, right?

If that is the case, you will need to get a few parts to get the job done. The best charger you would want to get for this type of set up would be part # RED96FR. Along with it you would need a 30-Amp MIDI Fuse Kit part # RED86FR as well as 23-Amp MIDI Fuse Kit part # RED76FR. You will also want to pick up part # RED66FR, this is a battery to fuse holder cable. This will help attach the MIDI fuses to the battery.

I've included a diagram so you can see how everything comes together.

In regard to the breakaway battery, I don't recommend removing that battery. It’s legally required to have a dedicated battery that can power the trailer’s electric brakes for at least 15 minutes in the event the trailer disconnects from the tow vehicle.

Back to the first part of your question you said that you were going to re-wire the trailer. Are you wanting to just replace the 7-way and junction box or are you wanting to replace all the wiring on the other side of the junction box as well? I ask as I've ran into situations where re-wiring meant just the trailer plug all the way to replacing all wiring and all of the trailer lights as well. Let me know if you need these parts as well.