Hey all, I'm just getting into camping with a travel trailer and was wondering if the batteries "automatically" charge while attached to the tow vehicle? I have verified I have 12v+ at the correct pin on the 7 pole trailer plug but got wondering if simply plugging in is the equivalent of putting two batteries together of different charge levels (which, if I understand correctly, is really bad on the wiring and the batteries as they equalize)? Is there supposed to be some kind of inline resistance to ensure nothing bad happens, or is it fine to have a wire directly from the tow vehicle battery to the travel trailer battery (through the connector of course)?

The camper battery will charge from your vehicle alternator, but the line connecting truck and trailer is small, so takes quite a while.Jerry

Most vehicles charge very slowly, in part because the wiring is limited. To see if you are getting anything check the batteries voltage 3 times. Once with the trailer disconnected, voltage at the battery. Second with the tow vehicle connected but not runningThird with the engine running. Your first and second voltages should be the same, the third after the tow vehicle has been running a few minutes should show an increase. If so, yes its charging as you drive.

YES ......Tow vehicle alternator will maintain/trickle charge trailer batteryProvided trailer battery disconnect switch (if so equipped) is ONOtherwise trailer battery 'could' be isolated from charge circuit (depending on how disconnect switch is installed)

cdoc83 wrote:Hey all, I'm just getting into camping with a travel trailer and was wondering if the batteries "automatically" charge while attached to the tow vehicle? I am sorry to say, that the other responders are very being very optimistic !At best, you can expect that the trailer batteries is NOT discharge any further. They certainly will not re-charge if depleted !Please read this DC-DC battery charger

It’s more of a maintainer circuit than a charge circuit. So if you have an inverter running like I do for my small dorm fridge then it will keep the trailer battery at the proper voltage. However it would take quite a while to fully charge a dead battery through the circuit.You also need to know if the vehicle side turns off power to the trailer when shut off so you don’t accidentally kill both battery’s.

Do batteries charge while driving? | Good Sam Community

MFL
Nomad II
May 03, 2018
The camper battery will charge from your vehicle alternator, but the line connecting truck and trailer is small, so takes quite a while.

Jerry
kerrlakeRoo
Explorer
May 03, 2018
Most vehicles charge very slowly, in part because the wiring is limited.
To see if you are getting anything check the batteries voltage 3 times.
Once with the trailer disconnected, voltage at the battery.
Second with the tow vehicle connected but not running
Third with the engine running.
Your first and second voltages should be the same, the third after the tow vehicle has been running a few minutes should show an increase. If so, yes its charging as you drive.
Old-Biscuit
Explorer III
May 03, 2018
YES ......
Tow vehicle alternator will maintain/trickle charge trailer battery

Provided trailer battery disconnect switch (if so equipped) is ON
Otherwise trailer battery 'could' be isolated from charge circuit (depending on how disconnect switch is installed)
theoldwizard1
Explorer II
May 03, 2018
cdoc83 wrote:
Hey all, I'm just getting into camping with a travel trailer and was wondering if the batteries "automatically" charge while attached to the tow vehicle?

I am sorry to say, that the other responders are very being very optimistic !

At best, you can expect that the trailer batteries is NOT discharge any further. They certainly will not re-charge if depleted !

Please read this DC-DC battery charger
dodge_guy
Explorer II
May 03, 2018
It’s more of a maintainer circuit than a charge circuit. So if you have an inverter running like I do for my small dorm fridge then it will keep the trailer battery at the proper voltage. However it would take quite a while to fully charge a dead battery through the circuit.

You also need to know if the vehicle side turns off power to the trailer when shut off so you don’t accidentally kill both battery’s.
time2roll
Nomad
May 03, 2018
To test put your voltmeter on the trailer battery. Then plug into your running vehicle. Voltage on the trailer battery terminals should pop up maybe a half volt if the vehicle charge system is putting power on the battery.

Just a slow charge due to vehicle voltage regulation and a long connection.
Maybe 5 to 12 amps into a low battery.
cdoc83
Explorer
May 03, 2018
First thing I'm going to do after work today! I guess it would be best to turn off the solar charger before testing anything?
theoldwizard1
Explorer II
May 03, 2018
time2roll wrote:
To test put your voltmeter on the trailer battery. Then plug into your running vehicle. Voltage on the trailer battery terminals should pop up maybe a half volt if the vehicle charge system is putting power on the battery.

Rev the engine up to a fast idle and you should get about 12V +/-1V at the trailer house batteries. Still not adequate to recharge your batteries.

cdoc83 wrote:
First thing I'm going to do after work today! I guess it would be best to turn off the solar charger before testing anything?

Yes !
cdoc83
Explorer
May 03, 2018
Cool, thanks! If it keeps the fridge from draining the battery while off propane I'll be happy!
RoyB
Explorer II
May 03, 2018
The Truck Charge system is very close to the truck start battery and will use the status of the truck start battery to produce charging DC Voltages.

Essentially this is saying the truck charge system doesn't know the trailer batteries are in the loop. This is primarily due to the small charge cable wire size going from the truck alternator setup to the trailer battery distribution panel.

Yes you will get some charging from the truck alternator system setup but I would only consider this a trickle charge status.

I'm sure those on here with more battery smarts than I have may have a better way of describing this in laymen terms...

Roy Ken