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Old 11-04-2021, 02:35 PM   #1
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To unplug or not...

I am wondering if when temporarily stopped, say overnight at a rest area, if I should unplug the trailer from the truck. The reason is I have a new fifth wheel with a residential style refrigerator. I have one battery with a inverter to power the fridge when not plugged to shore power. I am assuming when driving, the truck will keep the trailer battery charged which in turn will keep the fridge running? Also, back to my original question, if the trailer battery gets drained overnight, will it then take energy from my truck battery if I leave it plugged in? Which in turn would drain that battery also. Another question is can I add more batteries to the trailer, and are there more efficient batteries that I could replace them with...lighter and not needing to be vented?
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Old 11-04-2021, 02:44 PM   #2
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You've got a lot of questions there in your post!

But... to answer them we first must know what your tow vehicle is? (make/model/year)

Every manufacturer handles the power through the 7 pin connector differently.
Some have power all the time, some only when the key is on, some increase the alternator output when the 7 pin plug is plugged in, some increase the alternator power when the lights are on and so forth.

Give us some additional information. It may be in your signature or profile but they don't show on a mobile device using the app. (without having to chase it) Always put the pertinent information in the body of the post.
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Old 11-04-2021, 03:06 PM   #3
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Originally Posted by jjcooler65 View Post
I am wondering if when temporarily stopped, say overnight at a rest area, if I should unplug the trailer from the truck. The reason is I have a new fifth wheel with a residential style refrigerator. I have one battery with a inverter to power the fridge when not plugged to shore power. I am assuming when driving, the truck will keep the trailer battery charged which in turn will keep the fridge running? Also, back to my original question, if the trailer battery gets drained overnight, will it then take energy from my truck battery if I leave it plugged in? Which in turn would drain that battery also. Another question is can I add more batteries to the trailer, and are there more efficient batteries that I could replace them with...lighter and not needing to be vented?
That will totally depend on your truck. Best way to answer the question is to check the receptacle on the truck where the trailer is connected with a voltmeter. First with ignition on and then with ignition off.

If there is no voltage present when the ignition is off the trailer battery will not be able to draw power from your truck's starting battery as the charging wire is disconnected via an ignition controlled relay. If power is present then you will have to unplug.

Here's a diagram showing which terminal to check in the receptacle. The one marked "Charge" in the LH diagram labeled 7 blade Car (trucks use the dame diagram)




Some manufacturers wire the trailer receptacle so the charge wire is Hot all the time, some use a relay to kill the power when ignition is off. Many receptacles that are not factory installed have power there all the time.

Only way, again, is to check your vehicle using a voltmeter at the indicated pin even if you have someone with the same truck as yours tell you how THEIR truck is.
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Old 11-04-2021, 03:10 PM   #4
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Originally Posted by 5picker View Post
You've got a lot of questions there in your post!

But... to answer them we first must know what your tow vehicle is? (make/model/year)

Every manufacturer handles the power through the 7 pin connector differently.
Some have power all the time, some only when the key is on, some increase the alternator output when the 7 pin plug is plugged in, some increase the alternator power when the lights are on and so forth.

Give us some additional information. It may be in your signature or profile but they don't show on a mobile device using the app. (without having to chase it) Always put the pertinent information in the body of the post.
Thanks for the info...I have a 2012 Ford F250 Diesel with a 2021 Primetime Sanibel 3402WB
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Old 11-05-2021, 04:22 PM   #5
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Residential Freg.

You have to careful as the frig will kill a single RV battery and draw your truck batteries down in about 8 hours. I have dual group 31 batteries on my Hathaway 34RL, 8 hours will pull my batteries 50%. I had a battery go bad and my diesel was slow to turn over the next morning.
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Old 11-05-2021, 04:47 PM   #6
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My 2012 Ram with Cummins, is hot all the time at the 7 way plug. Easy to test as described above. For me - I will need to unplug, maybe, I don't have a 12v residential fridge, so it probably won't draw down the battery too much.

as far as lighter and stronger and able to mount without venting - LiFEPO4 batteries fit that bill, though they are on the expensive side up front.
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Old 11-05-2021, 04:51 PM   #7
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Another question is can I add more batteries to the trailer, and are there more efficient batteries that I could replace them with...lighter and not needing to be vented?
Yes - they are called LiFePO4 batteries. Here's a 100 AH LiFePO4 battery:
https://www.amazon.com/ECO-WORTHY-Re.../dp/B09FXJQ3Z3

One difference is that when a lead-acid battery is rated for 100 AH, you really only have 50 AH available because you should not discharge a lead acid battery below 50%. You get 100 AH out of a LiFePO4 battery rated for 100 AH.

The residential fridge consumes 15 amps max from 12v DC. So for 8 hours of operation you would consume 120 AH. That's not including any other loads such as lights, propane leak detector, furnace or vent fans.
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Old 11-05-2021, 04:58 PM   #8
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Originally Posted by jjcooler65 View Post
Thanks for the info...I have a 2012 Ford F250 Diesel with a 2021 Primetime Sanibel 3402WB
At some model year between my 2003 E350 and 2019 F150 Ford put in a relay so you could not discharge the truck battery if you left the trailer plugged into the truck overnight. Not sure what model year that started.
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Old 11-05-2021, 09:14 PM   #9
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I always disconnect the trailer from the truck over night...Better to be safe than sorry!!!!!!!!!!!!!!! Truck will always start in morning!!!!!!!! No boost required!
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Old 11-05-2021, 09:29 PM   #10
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Most trucks do not leave the tow circuit live when the motor is off. Been that way many years.

Easy to test. Turn the motor off. Unplug the rv and get the voltmeter out. Easy.

We often disconnect nothing when making 1 or 2 night stops. However, I have 4 gc2 batteries and a gas fridge. Love boondocking out west. Moab was really nice in September. Free sites everywhere.

You need lithium batteries and a decent battery monitor to go 24 hours without plugging in.

A built in automatic starting generator would be a good investment if you want to boondock.
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Old 11-05-2021, 10:07 PM   #11
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It takes 30 seconds to unplug the 7-pin connector and 30 seconds to plug it back in in the morning. With all the B.S. happening now in this country, you would be foolish not to double check everything before getting back on the road in the morning - electrical connections, the locking latch on the hitch (5th wheel or bumper pull), safety chains, heck - even check that lug nuts are at least finger tight. There are all kinds of internet "challenges" out there now calling for people to vandalize everything and anything.
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Old 11-06-2021, 07:42 AM   #12
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If I were you, I'd freeze a milk jug, put it in the fridge for overnight, and unplug the fridge. With one battery, and the fridge plugged in, you'd run down your battery in a hurry.
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Old 11-06-2021, 07:58 AM   #13
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Originally Posted by Jim in Halifax View Post
I always disconnect the trailer from the truck over night...Better to be safe than sorry!!!!!!!!!!!!!!! Truck will always start in morning!!!!!!!! No boost required!
Do the same, I have never checked to see if my check is powered all the time.

I also take the plug and pay it out along the bedside and into the driver's tire so I don't forget to plug back in the next morning.
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Old 11-06-2021, 08:03 AM   #14
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I forgot to unplug mine one night. Dead truck 2 days later. 2016 Ram 2500..
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Old 11-06-2021, 08:23 AM   #15
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I've never unplugged mine for over night or even days never an issue with truck battery .
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