Sunday, January 29, 2023


Does my RV still need a battery when connected to shore power?

Dear Dave,
I live in Montana. I remove my RV’s dual 12v batteries and bring them inside. Then I plug my trailer into shore power to run a small heater. I discovered that I cannot use my slide function without the batteries hooked up to the system. What is the purpose for wiring it that way? Shouldn’t it be set up to also work off shore power? —Mark, 2019 Northwood Arctic Fox 25W

Dear Mark,
Almost every slide-room mechanism uses 12-volt power to run the motor that extends and retracts the room. That battery is the house battery system, which could be two 6-volt batteries connected in series or a traditional 12-volt deep cycle battery. The 12-volt power is provided by that battery bank through the distribution center and a fuse to the slide room motor or motors. The house battery/batteries are charged by a converter, inverter/charger, or solar panels.

What’s the type of converter and how are the batteries wired?

To answer your question, we need to know the type of converter you have and look at how the batteries are wired. Converters are simply battery chargers and some of the new chargers need to have an actual connection or battery as a buffer. I just purchased a new battery charger from NAPA. A neighbor left their lights on so the automotive battery was dead. I hooked up the charger and nothing! Since the battery had gone below 2 volts, the charger has a safety feature that prevents touching the two leads and creating a spark, so it will not turn on until it senses voltage. That means you need a battery between the leads. I had to install a 12-volt power supply I use for bench testing to get it up to a few volts, and then the charger kicked in.

However, the WFCO converter we pulled out of the 2015 Thor Challenger will provide 13.6 volts with nothing connected. We installed lithium batteries and changed out the WFCO with a Progressive Dynamics model recommended for lithium. I would suggest finding your converter and use a multimeter to see if there is 12-volt power coming out of the converter without the batteries connected. Your converter will either be an all-in-one as part of the distribution center, or be a standalone, like ours was.

This converter will provide 13.6 volts when it senses a low battery or no battery at all. It then drops to 13.2 volts when the battery is fully charged, as this is the maintenance or float charge. If you do not have voltage coming out of the converter, it is the voltage-sensing model and will not provide 12-volt to the distribution center.

But if it provides voltage

If you do find it provides voltage, the next place to look is the wiring or cabling at your battery center. Some RV manufacturers use several cables going to different relays and battery isolation management (BIM) systems or solenoids. If you removed cables, it may have created an open circuit and you will need to connect all the positive cables together.

This was the rat’s nest that was in the Thor. You can see there are two cables on the positive side that would need to be connected to provide power to the distribution center if the batteries were disconnected.

 You might also enjoy this from Dave 

How should the RV’s 6-volt and 12-volt batteries be wired?

Dear Dave,
I have a Class A diesel pusher motorhome with two 6-volt and two 12-volt batteries. How should these batteries be wired? Any info on this would be appreciated. —Carla, 1999 Overland Lorado

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here


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1 month ago

I live in Montana also (forecasting -28 F. in 2 days) and never take my house batteries out of my MH. I connect a 1.25 AMP Battery Tender Plus 12V charger maintainer to the house batteries connected in parallel. It keeps the batteries fully charged without over charging (it’s either a 3 or 4 stage charger). My batteries are 4 years old and the Battery Tender hasn’t failed (of course check the level in each cell). Every 2 weeks I allow the batteries to discharge, then I reconnect the Battery Tender. Open to suggestions if I should be doing something different.

Thomas D
1 month ago

He’s supplying power for the heater, use the same power to run a battery maintainer. I just clamp on to the battery terminals and forget about it. If dubious, kill the power to the house converter. A little 800 ma maintainer keeps my 2batteries fully charged without the work of physically removing 90# batterys

1 month ago

You need to consider the other side of the equation – Amperage. The slide motor draws more current (amperage) than the converter can supply. A battery/batteries can supply a great deal of current where the converter only supplies a limited or low amount of current. When the battery is connected you have ample current supply to run the slides. Remove the battery and the converter cannot supply the needed current so the slide will not work.

1 month ago

I remember years ago that there is a battery connector bar that you connected to the positive and negative clamps if you removed your battery to complete the electrical system to work all 12v systems in the RV. Don’t know where to get one as I have/had no need for one. I would check with people smarter than I if that can still be done. Mike would know as electrical is his thing.

Bob p
1 month ago

If he has a large enough battery charger he could possibly connect t to the battery cables and it may work, my battery charger won’t work unless it’s connected to a battery, this is a safety feature I guess.

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