Tow Vehicle Battery Question...

[ski boy]

Anyone happen to know if the tow vehicle's battery powers the trailer's 12V circuits if you leave the cable between the two vehicles hooked up while dry camping? I know that the old travel and tent trailers decades ago got all their 12V power off the car battery (no battery on some of the old trailers in those days...)

[bfast54]

On most older vehicles, that would be a YES.


Newer vehicles MIGHT have a disconnect, with a relay that turns power off, from the tow vehicle, to the trailer when key is off. But I would guess, based on experience, it would drain it if left connected for a long period, if trailer not hooked to shore power.

You could check it , on your vehicle by turning your tow vehicle off, and using a 12 volt test light, check "charging" pin on your tow vehicle plug .

If I am going to be parked for a while, with truck still hooked up (days , not hours) I unplug the 5er from the truck.

[campswithcritters]

02 & 05 Dodge were both only powering trailer when truck key was on, 07 Chevy & 08 Freightliner were same way too. I never bothered to unplug any of my tow vehicles and never had a problem. When ever we leave it hooked that long the trailer is on shore power and the converter would charge the truck battery in any case.

[bigbunkhouse]

all the Fords I work on also only power when in RUN, quite often I will hit my remote start on my work truck to get the 12volt lights to work in the utility trailer as I am cleaning up in the dark.

[ski boy]

I was a little concerned about how much juice needs to be left in the trailer's batteries to operate the slides - the manual says that they need full power. I checked, with a tester, to see if there is any current from the TV cable if the engine is shut off - none - as everyone has said - works only if the key is on...I assume that, if the batteries were run down enough that the slides wouldn't come in, you could plug in the TV and turn on the engine - Truck's batteries would provide enough power to run the slides in. Make sense?

[bfast54]

The only fly in that oinment is....................if the trailers batteries are run down so far the slides wont work, I dont think the power you would be getting on the "Charge Circut" from the tow vehicle , to the trailers batteries, would be enough.

Since you have a small wire, and you are only able to charge, as it were................not run full power to the batts. You may need to plug the rig in, and charge the batts from the comverter, or use a batt. charger, or Boost .........to raise enough Volts-Amps. It takes some considerable amps to run the slide motor.(and a low battery, with just a trickle charging/avail might not be enough).

Do you Follow my 12 volt thinking

[campswithcritters]

The only fly in that oinment is....................if the trailers batteries are run down so far the slides wont work, I dont think the power you would be getting on the "Charge Circut" from the tow vehicle , to the trailers batteries, would be enough.

Since you have a small wire, and you are only able to charge, as it were................not run full power to the batts. You may need to plug the rig in, and charge the batts from the comverter, or use a batt. charger, or Boost .........to raise enough Volts-Amps. It takes some considerable amps to run the slide motor.(and a low battery, with just a trickle charging/avail might not be enough).

Do you Follow my 12 volt thinking

Is true! Ran my batt down once, truck only supplied 30 amps (fused) so quickest way to get slides in was to turn truck around and apply jumper cables, worked like a charm!

[ski boy]

Just for clarification...I understand, now, that the TV batteries probably will not provide enough power through the cable to run the slides. Questions - Do the batteries on the TV charge the trailer batteries when going down the road (trickle charge?) Do the brake and lights circuits for the trailer operate off the trailer batteries or directly off the TV batteries? I can't believe I never thought about this before. (I like the idea about the jumper cables - that would have never occured to me!)

[campswithcritters]

Just for clarification...I understand, now, that the TV batteries probably will not provide enough power through the cable to run the slides. Questions - Do the batteries on the TV charge the trailer batteries when going down the road (trickle charge?) Do the brake and lights circuits for the trailer operate off the trailer batteries or directly off the TV batteries? I can't believe I never thought about this before. (I like the idea about the jumper cables - that would have never occured to me!)

The truck alternator/batteries will provide up to the limit (fuse) amps charging while on the road. If your trailer battery(s) dead most of that flow will go toward recharging the dead cells and any high draw items will still not work unless you up the charge path as in jumper cables. The brake & light circuits run entirely off the truck electrical system until (hopefully not) the trailer comes disconnected then the trailer battery is responsible for emergency braking (ie the break-away cable is pulled).

[bfast54]

Just for clarification...I understand, now, that the TV batteries probably will not provide enough power through the cable to run the slides. Questions - Do the batteries on the TV charge the trailer batteries when going down the road (trickle charge?) Do the brake and lights circuits for the trailer operate off the trailer batteries or directly off the TV batteries? I can't believe I never thought about this before. (I like the idea about the jumper cables - that would have never occured to me!)

No, the batt on the tow vehicle does not charge the trailer batts while going down the road.The Vehicle Alternator charges it.

The lights on the outside, and brake, turn signals run off the Tow Vehicle, there is no Direct connection to the trailer battery. If you turned off the tow vehicle, with the Marker, running lights on, and left it, it WOULD run down your Tow Vehicle battery, it would not touch the trailer battery.


Hope that helps to clarify it.

[bfast54]

Wow Bruce......Talk about Great Minds thinking together!!!!!!! ............

[campswithcritters]

Wow Bruce......Talk about Great Minds thinking together!!!!!!! ............

That ought to cover the question for sure and no more need for a second opinion!