How to Charge the Batteries on a Trailer While Underway

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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

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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

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Answer 1

In order to determine the torque rating for the lug nuts on your trailer you will need to know check out the chart I attached that shows all of the torque specs for all the trailer lugs available based on stud size, wheel material and wheel size.

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Answer 2

The difference between the Class II and Class III hitches has to do with their Gross Trailer Weight (GTW), their Tongue Weight (TW), and their Hitch Receiver Size. Class II trailer hitch receivers have a 1-1/4 inch receiver and can be rated up to…

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Answer 3

A 4-Way trailer connector has the basic lighting functions only; running lights, left turn signal and brake lights, right turn signal and brake lights, and ground. A 7-Way has these functions and a 12 volt circuit, a circuit for electric trailer…

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Answer 4

You would not be able to charge your battery through the wiring on your 4-way trailer connector. Since your truck has a 7-way connector, you could maintain the power to the battery but not charge it. To begin, you would need to cut off your 4-way…

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Answer 5

That's a very good question, we tend to be extra cautious and say to use 10 gauge wire because that would be more than enough. When you get into longer trailers that will end up using a lot of wire the heavier gauge wire becomes more necessary.…

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Answer 6

The difference between an load range C and load range D tire in the same size is the capacity and psi rating. The two tires will still have the same dimensions and fit on the same wheel. The D rated tire has a higher capacity. For a ST175/80D13 like…

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Answer 7

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Answer 8

The three most common lug stud sizes for a trailer are 1/2"-20, 9/16"-18, and 5/8"-18. In order to make sure you get the correct lug nuts you need to measure the lug studs on the trailer now as we have no way to look this up for…

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Answer 9

First you will need to remove the old hydraulic equipment. Remove the surge coupler or actuator, remove all the lines, and finally remove the brake assemblies. If you have 10 inch diameter hub and drums, you may need to replace those as well. If you…

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Answer 10

The best way to power the interior lights in your trailer is with its own independent battery. You will not want to use the breakaway battery. The breakaway battery is only designed to operate the breakaway and will drain extremely quickly,…

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Answer 11

You are correct in your description of how to wire in a new auxiliary battery in your enclosed trailer. You will take the 7-Way's 12V power feed and route this to the positive terminal on the auxiliary battery, and you will ground the second…

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Answer 12

To change the battery mode on the Progressive Dynamics 9300 Series RV Converter Charger #PD79RR you'll need to insert the included CLAW tool into the small opening next to the battery type indicator light. Press and hold that button (using the…

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How to Charge the Batteries on a Trailer While Underway

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