Flat Towing Battery Drain: Why the Toad’s Battery Dies and How to Prevent It

By Jeff McDonough, Founder of TowPro Academy, 10+ years and 250,000+ miles of towing experience.

Short answer: A flat-towed car’s battery usually dies because the tow procedure leaves the ignition in a position that keeps the steering unlocked and some electrical circuits awake, and a supplemental braking system can add its own draw. Over a full day of driving that adds up. The fix depends on your vehicle: some makers tell you to pull specific fuses, some tell you to disconnect the battery, and at least one tells you never to disconnect it and to feed the battery from an outside 12-volt source instead. Your owner’s manual decides which one applies to you.

This is one of the most common complaints from new flat towers, and most of the answers online are forum threads. Here’s how the problem works and what the vehicle makers themselves say to do about it.

Why the toad’s battery drains while you tow

When you drive a car, the alternator keeps the battery charged. When you flat tow it, the engine is off, so nothing is putting charge back in. Meanwhile, three things can be pulling power out:

• The ignition position. Many tow procedures require the key or push-button ignition to stay in accessory (ACC) or a similar mode so the steering column doesn’t lock. MotorHome magazine’s 2019 Guide to Dinghy Towing explains that this keeps power applied to various electrical circuits, and over a full day of towing that “can lead to significant battery discharge.”
• Modules that stay awake. Body control modules, the engine computer and other electronics can keep drawing current in that mode. That’s why some makers name exact fuses to pull.
• A supplemental braking system. Some add-on brake systems draw power from the towed car. Ford’s 2026 Bronco owner’s manual warns that if you use an add-on flat tow braking system, “the battery may discharge during the remainder of the tow.”

Put those together on a 300-mile travel day and you can unhook at the campground to a car that won’t start, or worse, one whose electronics behaved oddly while it was behind you.

What the makers actually tell you to do

There is no single right answer, and that’s the trap. The fix that saves one car’s battery can cause a real problem in another. Here are three real examples from manufacturer instructions, so you can see how different they are.

1. Pull specific fuses (some GM models)

The 2019 dinghy guide’s chart, which summarizes each maker’s procedure for that model year, lists fuse pulls for several GM vehicles. For the 2019 Buick Envision it says to prevent the battery from draining by removing fuses 29 and 32 (BCM) from the instrument panel fuse block. For the 2019 Chevy Traverse it lists removing two named fuses from the engine compartment fuse block and putting them back once you reach your destination. Those fuse numbers are specific to those models and years. Don’t copy them to your car.

2. Disconnect the negative battery cable (some 4WD trucks and SUVs)

For some 4WD models in the same chart, such as the 2019 Chevy Colorado 4WD and Cadillac Escalade 4WD, the listed procedure includes disconnecting the negative cable at the battery, securing the nut and bolt, and covering the negative post with non-conductive material. That takes the battery out of the circuit entirely while you tow.

3. Never disconnect the battery (2026 Ford Bronco)

Ford’s 2026 Bronco owner’s manual carries a warning: do not disconnect the battery when recreationally towing, because it prevents the transfer case from shifting properly and could cause the vehicle to roll. It also notes that the transfer case can switch out of neutral when battery voltage is low. Its fix for brake-system drain is to connect a 12-volt external power source to the towed vehicle’s battery for the duration of the tow.

Read those three side by side and the lesson is clear: “just pull the battery cable” is great advice for one vehicle and dangerous advice for another. A low battery isn’t only an inconvenience at the campground. On some vehicles it affects how the drivetrain behaves while it’s being towed.

Your options, and when each one fits

A charge line helps the battery, but it doesn’t replace any step in your tow procedure. If the manual says to pull a fuse and your brake system draws power, you may need both. Have a charge line installed by someone who does RV electrical work, with proper fusing at the coach end, and confirm it’s actually charging with a voltmeter at the toad’s battery the first time you use it.

Arriving to a dead toad battery

If you unhook and the car won’t start, slow down before you reach for jumper cables:

1. Finish the unhook procedure first. Make sure the vehicle is secured and back in the state your manual calls for (park, parking brake, transfer case out of neutral if that applies) before anything else.
2. Reinstall any fuses you pulled and reconnect anything your procedure had you disconnect.
3. Jump or charge it the way the owner’s manual says. Many modern cars have specific jump points under the hood.
4. Check for settings that reset. Some manuals warn that disconnecting or losing battery power affects things like the anti-theft system or window and radio memory. Your manual lists them.
5. Figure out why before the next tow. Was a fuse missed, was the ignition left in the wrong mode, or is the brake system drawing more than expected? A dead battery on day one will be a dead battery on day two.

Build it into your hookup routine

The 2019 dinghy guide’s own hookup checklist includes the step “ensure the appropriate fuses are pulled or the battery disconnected, if applicable.” I’d add two more lines to any toad checklist:

• Ignition left in exactly the position your manual specifies, and nothing else switched on (lights, climate fan, phone chargers).
• At the first fuel stop, check that the toad’s battery state looks the way it did at departure, especially on a new setup.

Some procedures also call for running the engine at set intervals (the 2019 chart lists this for the Traverse, for example). That’s for the transmission, not the battery, but it’s another step that belongs on the same checklist. Our free pre-trip towing checklist is a good place to start, and our guide on how to flat tow a car behind a motorhome walks through the full hookup.

For a printable version with blank lines for your own vehicle’s steps, use our flat towing checklist.

Related flat towing guides

• Can My Car Be Flat Towed? Start here if you haven’t confirmed your vehicle.
• Supplemental Brakes for Flat Towing
• Flat Tow Baseplates and Tow Bars, Explained
• Flat Towing a Jeep Wrangler or Ford Bronco
• Flat Towing a Honda CR-V or Chevy Equinox
• Flat Tow vs. Tow Dolly vs. Trailer

FAQ

Will flat towing drain my car’s battery?
It can. If your tow procedure leaves the ignition in accessory mode or your braking system draws power from the car, the battery can run down over a long day. Whether it does depends on the vehicle and the setup.

Should I disconnect the battery when flat towing?
Only if your owner’s manual says to. Some makers list it as part of the procedure. Ford’s 2026 Bronco manual says not to, because it affects the transfer case.

Do I need a charge line?
Not always. It’s most useful when your vehicle can’t have its battery disconnected, or when a brake system or required ignition mode draws power for hours. It doesn’t replace any step in your manual’s tow procedure.

Which fuses do I pull?
Only the ones your owner’s manual names for your model year. Fuse numbers differ between models and years, so never copy them from another vehicle or a forum post.

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