How to Charge the Batteries on a Trailer While Underway

Updated 06/29/2022 | Published 06/25/2022

Products Featured in This Question

Starter Solenoid - SPST - 12 Volt - 100 Amp - Continuous Duty - Grounded

(14)

$35.41

Redarc In-Vehicle BCDC Battery Charger - Dual Input - DC to DC - 12V/24V - 25 Amp

(87)

$484.59

40-Amp MIDI Fuse Kit for Redarc In-Vehicle 25-Amp BCDC Battery Charger

(18)

$90.00

Question:

Engaging this subject again...been reading other threads on using tow vehicles alternator to charge the trailers batteries, and have come to the conclusion that it will maintain them, but not necessarily charge a discharged battery very well. My thoughts here are the run a 4 gauge wire from the vehicle electrical system to the trailer via a battery isolater. If thats done, can I expect the battery bank to be maintained at near full charge between destinations, or is the slow rate of charge from the vehicle electrical circuit going to have a minimal effect? I have a residential fridge to power via an inverter when traveling. My goal here is to keep the battery as near full charge when traveling to prevent the high draw on the generator when we arrive and the inverter charger kicks on to charge the house batteries, reducing the need to run two generators paralleled to power AC, inverter/charger, and other electronics.

asked by: Steve C

Expert Reply:

You are correct that the power coming from your vehicles battery while traveling is only going to provide a maintenance charge to your batteries on your trailer. It will not charge a dead battery and it will not keep the trailers batteries charged if they are being used while underway. Using wiring and a solenoid like the # PK5231201 that you mentioned will provide a good maintenance charge while you're driving but that is about it.

In order to charge and maintain a full charge you will need to use a battery charger like the Redarc In-Vehicle BCDC Battery Charger # 331-BCDC1225D. This will connect directly to your tow vehicles battery to provide 25 amps of current to the trailer battery. It also has a built-in battery isolator that will prevent the charger from pulling any power from the vehicles battery when it's off. We also have the 40-Amp MIDI Fuse Kit for Redarc In-Vehicle 25-Amp BCDC Battery Charger # 331-FK40 available for installation.

I have attached an installation video that you can also check out to get a better idea of how it works.

expert reply by: Scott S