Thread Tools Display Modes
Old 04-03-2017, 03:11 PM   #1
Junior Member
Join Date: Jan 2017
Posts: 25
Charging batteries while towing

Ok... So I'm sure someone has already asked this question before but I searched and couldn't find it or an answer so here goes...

If your camper is hooked to your truck (towing vehicle) and your towing vehicle is running is there any voltage going to the batteries on your camper to keep them charged while you drive down the road? If so does it matter or make a difference if the master battery switch is on or off?

SCSTTROOPER is offline   Reply With Quote
Old 04-03-2017, 03:19 PM   #2
Senior Member
Join Date: Feb 2017
Location: SW Ohio
Posts: 682
as long as you have the round 7 connector plug there should be power, on my truck I needed to plug a relay in to get it. it may be switched with the ignition or not, if not it could drain the truck battery when towing.

it should be connected to the trailer battery & the breakaway switch. past that point it doesn't really matter but I would leave it connected to the coach to run the fridge, convenience for quick stops etc

llr is offline   Reply With Quote
Old 04-03-2017, 03:22 PM   #3
Pickin', Campin', Mason
5picker's Avatar
Join Date: Aug 2015
Location: South Western PA
Posts: 8,221
The short answer is yes, provided you have a 7 pin connector, your tow vehicle is correctly wired and has the fuse/relay installed. (not always installed from the factory)

Remember the wires from the alternator to the battery in the trailer are small so you'll get a trickle charge at best but it will provide some charge.

To your question about the disconnect switch... depends.
We read reports of disconnect switches being wired 12 different ways to Sunday.
A voltmeter test on the trailer battery (engine on/engine off) is the only way to tell for sure.
2016 Flagstaff 8529IKBS Diamond Package 5th Wheel-Goodyear Endurance Tires
2017 Ford F-Series SCREW 4x4 - Factory Puck
TST Tire Monitor w/Repeater - Sinemate 3500w Gen.

Days Camped: '15=22 '16=46 '17=30 '18=51
5picker is offline   Reply With Quote
Old 04-03-2017, 03:27 PM   #4
Senior Member
mikakuja's Avatar
Join Date: Nov 2016
Location: British Columbia, Canada
Posts: 161
Without knowing how your vehicle or trailer is wired it is hard to answer your question. That being said, (in most cases)yes you will have 12v to the trailer from the TV (with a 7pin connector) but not enough amperage to do much in the way of charging due to the small wire size.

Battery shut off is another thing altogether, hard to say without knowing how it is wired. Some testing is needed here.

2017 Surveyor 245BHS
2011 F250 6.2L Crew SB 4X4
mikakuja is offline   Reply With Quote
Old 04-03-2017, 03:48 PM   #5
Site Team
bikendan's Avatar
Join Date: Jan 2007
Location: Camano Island, Washington
Posts: 17,069
most tow vehicles only supply a trickle charge at best.
Dan-Retired California Firefighter/EMT
Shawn-Musician/Entrepreneur/Wine Expert
and Zoe the Wonder Dog(R.I.P.)
2016 PrimeTime TracerAIR 255, pushing a 2014 Ford F150 SCREW XTR 4x4 3.5 Ecoboost w/Max Tow Package
Equalizer WDH
bikendan is online now   Reply With Quote
Old 04-04-2017, 01:03 PM   #6
Join Date: Nov 2013
Posts: 78
Generally, most vehicles are not wired to provide this charge. You can check a wiring diagram for your vehicle or check with a voltmeter at the plug. As stated before, you must have the "Barger" 7 wire plug to generally have this capability. If it is a 4 wire connection, then you don't.

Here is the wiring diagram

Personally, I wire a new line running from the tow vehicle battery back to the tow plug. Use at least 10 gauge, preferably 8 gauge, with an auto-reset 10 Amp circuit breaker right up by the battery. You will also need to verify that the trailer side also has wiring. Typically, you will if you have a trailer with a battery for the brake system. That should also be protected with a circuit breaker near the battery of the tow vehicle, since you don't want a short in that line to fry your trailer. You can also add an in-line charger for that purpose such as


2005 Coachmen Sportscoach Encore 380DS
2014 Jeep Wrangler Rubicon Unlimited
CharlieS3 is offline   Reply With Quote
Old 04-04-2017, 01:50 PM   #7
Junior Member
Join Date: Jan 2017
Posts: 25

1) The 7 pin plug on my 2017 GMC Sierra does have the ability to provide 12+ volts to the camper.

2) The pins on the 7 pin plug that provide the 12V power are not switched with the key and remain hot all the time even if the vehicle is not running.

3) The two pins of the 7 pin plug have a dedicate (30 amp) fuse under the hood just for those two pins.

I can't imagine that connector and the small wire associated with it providing 30 amps but that's what the fuse is rated for.
SCSTTROOPER is offline   Reply With Quote
Old 04-04-2017, 02:03 PM   #8
Senior Member
Join Date: Feb 2016
Posts: 154
There is an easy to check if your are getting charging voltage from your tow vehicle.. if you have a 12v plug in inside your RV, you need to buy one of these:

With the tow vehicle disconnected from the RV, you should read only RV battery voltage.. Once you plug into the tow vehicle, with the engine running, it should give you a great reading, around 13 + volts..
Also you can keep an eye on the RV battery voltage when dry camping..and charge your phone etc with this meter..
2015 F350 4x4 gasser.. 2017 Rockwood 2506S TT
Ardenvoir, Washington (near Wenatchee)
clintbonnie73 is offline   Reply With Quote
Old 04-04-2017, 02:18 PM   #9
Senior Member
dbledan's Avatar
Join Date: Jan 2017
Location: KS
Posts: 1,207
On newer F150s 2016 they don't supply voltage until they detect current draw. The truck throws an error if I have the battery cutoff turned off saying it cannot charge and to check the wiring. The way the trailer battery is wired would determine if this is the case for your rv.

You cannot just test the pins to know with this setup as you actually need to check it with the trailer connected.

Clintbonnie73 is right. I have a similar gadget I put in the lighter socket inside the trailer to know how the battery is doing and if I am getting a charge from TV. Of course any volt meter would work.
dbledan is offline   Reply With Quote
Old 04-04-2017, 02:23 PM   #10
Just as confused as you
Scrapper's Avatar
Join Date: Aug 2013
Location: Rio, Wisconsin
Posts: 2,715
By my understanding if you have the trailer towing button on the gear shift lever pushed then the computer in the 2011+ GMC/Cheverolet will boost the output of the alternator. The owners manual will explain it all for you.

My 2011 Silverado has this feature.

Richard & Jill
2014 Flagstaff 832IKBS Classic Super Lite
2018 Silverado 1500 Crew Cab Z71 4WD All Star Edition
Camping since 1989, seasonal since 2000
Car Shredder Operator/Technician, Scrap Metal Recycling - retired
Scrapper is offline   Reply With Quote

batteries, charging, towing

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

» Featured Campgrounds

Reviews provided by


This website is not affiliated with or endorsed by Forest River, Inc. or any of its affiliates. This is an independent, unofficial site.

Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 01:34 PM.