Tow vehicle battery drain

[greyhound10]

I am towing a 2018 Whitehawk27rb with a 2018 Ford F150 XLT. I recently stopped for gas, and when I tried to restart the truck, it appeared the battery was nearly dead and the truck wouldn't start. I had the truck checked at a battery shop, and the battery and charging system was ok. All of the trailer running lights and brakes were working fine. The trailer battery charges ok. I use a digital voltage gauge plugged into the 12v plug inside the camper. I have never had this happen in thirty years of towing. Anyone have any ideas what would cause this?

[Happy wife / happy life]

Just a guess. Has anyone check the connections at the starter? I would also check the ground battery cable . Is it clean and tight at both ends ?

[greyhound10]

Thanks. That's a good idea. The truck does start up normally when not connected to the trailer.

[craigav]

When you tried to start the truck, did the starter turn over the engine slowly or any at all, or was it that the starter wouldn't even engage? ~CA

[greyhound10]

The starter turned over, but there wasn't enough battery to start the engine.

[jeffmcpa]

Anything in the trailer running on 110v through an inverter while you are towing? If so, is it possible that is sucking more your TV alternater can handle?

[Yooper906]

Originally Posted by greyhound10

The starter turned over, but there wasn't enough battery to start the engine.

This sure sounds like battery or starter connections. Or a high amp starter draw?
I doubt being plugged into the trailer is draining the battery that much. I've left mine plugged to the truck overnight and haven't had any problems, but wasn't running the inverter.

[Happy wife / happy life]

When you were told that the battery and charging system was ok were they checking it with trailer hooked up? Have you noticed the in dash volt meter needle fluctuating ( above and blow 12 volts)? I’m just trying to eliminate a weak voltage regulator. You may also look at the serpentine belt tensioner, if it has a weak spring it may not be putting enough pressure ( under a load)on the belt to keep the alternator fully engaged.When you get this figured out would you post what the problem was? You have my curiosity up. Best of luck on this one!

[16WhiteColly]

If I suspect a bad ground, I hook up one jumper cable to the Neg. cable end and to a known good metal ground just to see if it makes any difference.

[ARoamer]

Only a fuel stop should not drain your TV battery. If battery checks out fine I agree with others to look for bad connections.

[craigav]

Once upon a time I owned a Ford truck that would always have an issue with the starter when the engine and starter were hot (as may be the case for the OP). I replaced the starter and thought I had it all under control until it happened again, but only when the engine and area around the starter was hot (not an overheated engine). I ended up shielding the starter from the exhaust manifold and no longer had any issues.

Point being, perhaps it is not the battery or voltage that is low, but a dragging starter. The only way to really know is to test the amp draw when the issue occurs, but certainly a check of all the cables and connections would certainly be something to check early on (first). ~CA

[Texas Tim]

My '18 F-150 XLT 4x4 does this exact thing sometimes, but not always and even when I'm not pulling a load or have a trailer plugged into it. Usually happens when I stop for gas too. I wonder if there is some validity to the "starter getting hot" from the exhaust manifold. I'd like to know if you find out what the issue is as I haven't been able to figure it out. Thanks!

[Oscar348]

Mine did the same thing last year. I had to replace the 7 pin connection on my bumper. It had gotten wet and was all rusted and corroded inside. It happened on a cross country trip. During the trip I had to disconnect the 7 pin while I had the truck shut off. And plug it back in after I started it. Once I changed out the male connection on the truck there were no more issues.

[berwin]

Does your tow setup have a feature that charges the thing being towed? My Jeep Wrangler had a line from the tow umbilical to the battery to keep the toad charged and I know many trailers have this same setup.

[Wireman]

Originally Posted by greyhound10

I am towing a 2018 Whitehawk27rb with a 2018 Ford F150 XLT. I recently stopped for gas, and when I tried to restart the truck, it appeared the battery was nearly dead and the truck wouldn't start. I had the truck checked at a battery shop, and the battery and charging system was ok. All of the trailer running lights and brakes were working fine. The trailer battery charges ok. I use a digital voltage gauge plugged into the 12v plug inside the camper. I have never had this happen in thirty years of towing. Anyone have any ideas what would cause this?

Did they load test the battery?
Is it the original OEM?
Is this the first time it's happened?
Strange it's only with the TT hooked up.

[muckinfuss]

This is how you determine if the trailer is at issue: While all hooked up, engine running and trailer in daytime 'tow' mode (everything off you would normally have of and anything on that you would tow while on) use a claw amp multimeter. Put the claw around the pigtail at least a foot from the 7 pin and take a reading. It should be very low...maybe half an amp.

Take a second read with lights on. It will read considerably higher if you are still lit up with incandescent and perhaps 2 amps if every single bulb in the running lights are LED.

example Ave. 12 volt draw:
LED each .25 amp
CO/Gas detector .15

If the trailer checks out fine with no suspicious draw, then the first thing I'd do is get a second opinion on the alternator in your truck. One hot diode in the internal regulator can be overlooked in the simple non-load output test on a cool engine and is more likely than some ground issue since grounds don't draw current, they let it flow when being drawn.