How to Charge a Trailer Battery While Driving: 3 Common Problems (And How to Fix Them)

A dead battery can be more than an inconvenience—when it comes to your trailer, letting your battery charge drop too low can permanently affect its ability to hold a charge. Not to mention, dealing with a dead trailer, tow vehicle, or accessory battery is a huge pain that can put a damper on your trip.

The truth is, any time you're dealing with a trailer, maintaining battery health is crucial. Below are three common problems our customers run into when it comes to their batteries, as well as our recommended solutions.

Discover what to do if:

Your Trailer Battery Doesn't Fully Charge
Your Trailer Battery Drains Your Tow Vehicle Battery
You Need to Charge Your Winch or Dump Trailer While Driving

Battery Health

A note on battery health before we begin—always monitor your trailer battery's charge to ensure it doesn't drop below 50%. Dropping below a 50% charge will shorten the lifespan of the battery. If you don't have a built-in indicator, a battery monitoring system can provide the status of your charge.

My Trailer Battery Doesn't Fully Charge

If you've ever tried to charge a dead trailer battery with just your vehicle and a 7-way connector, you know that this plan is doomed to fail. The distance between the vehicle battery/alternator and the camper battery is simply too far to fully charge a trailer battery from a depleted state. The most you can do is provide a maintenance charge to prevent your trailer battery from being DOA at the campsite, and even this will only charge your battery to about 80%.

So can you actually charge your trailer battery with your vehicle's alternator? Yes—but you'll need more than a 7-way.

To charge your trailer battery, you'll need a DC to DC battery charger. These chargers typically connect directly to your batteries (rather than your 7-way) to provide the power needed to charge your trailer battery from a depleted state.

In addition, many models are designed to draw power from both your vehicle alternator and solar panels, if they're available. So these chargers are excellent choices for keeping your batteries charged while driving or boondocking.

Redarc BCDC Battery Charger

Brings battery to 100% without overcharging (compared to about 50% through 7-way)
Won't drain tow vehicle battery
Green Power Priority ensures power is pulled from available solar panels first, only tapping into vehicle battery when necessary

Required to Install:

Fuse Kit: # 331-FK40 (for # 331-BCDC1225D) or # 331-FK60 (for # 331-BCDC1240D)
Wiring Kit: # SW1520

Watch: Video Install

My Trailer Battery Drains My Tow Vehicle Battery

Those of us who have ever left our vehicle lights on overnight can attest that dead batteries are terribly inconvenient.

Even worse than a dead battery in the driveway, however, is a dead battery in the middle of nowhere, two days into your boondocking adventure. Unfortunately, if you use your 7-way connector to maintain your trailer battery and don't disconnect (or use a battery isolation solenoid) once you shut off your vehicle, then this is exactly what you can expect.

You have a couple of options here. The first is to simply disconnect your trailer from your vehicle when you reach the campsite. Another option is to use a battery isolation solenoid so that power is only drawn from the vehicle battery when the vehicle is running. Isolation solenoids are a simple, economical way to preserve your vehicle battery, so you never have to worry about forgetting to unplug. You can also use a battery charger with a built-in isolation function. A battery charger has the added benefit of fully charging your trailer battery while you drive.

I Need to Charge My Winch or Dump Trailer While Driving

Unfortunately, 7-way connectors don't provide a sufficient charge to power a winch or dump trailer, but you can keep a winch or dump trailer charged by drawing power from either the tow vehicle battery or trailer battery.

Option 1: Draw From Vehicle Battery

The first option is to install a winch wiring kit to connect the winch or dump trailer directly to your tow vehicle's battery (without splicing into the 7-way).

You'll also want to use a battery isolator to prevent your vehicle battery from draining when the ignition is off.

Option 2: Draw From Trailer Battery

Although it's not a good idea to power your winch or dump trailer directly from your 7-way connector, you can use the 7-way to keep your trailer battery topped off. Then you can use your trailer battery to power the winch or dump trailer.

Or, for maximum efficiency, charge your trailer battery with a charger like the Redarc BCDC. Then use the trailer battery to power the winch or dump trailer.

Warning: We recommend unplugging the 7-way connector before using the dump feature on a dump trailer. Leaving the 7-way plugged in while dumping the trailer can potentially short out the 12-volt accessory circuit.

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