Dave Solberg

RV Battery Maintenance: Checking Battery Charge

Dave Solberg
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RV battery maintenance has just become easier! The 12-volt deep cycle battery or batteries of your house system must be properly charged to prolong their life and reduce sulfation. You can check not only the current state of charge in your house batteries but also the charging system of your converter with a multi-meter.

House batteries are typically located in a vented compartment on the side of an RV or inside underneath the steps in the case of basement models. Travel trailers usually have the 12-volt deep cycle house batteries on the trailer tongue, and fifth wheel house batteries are in a front compartment.

Use a simple multi-meter connecting the red wire to the positive side of the battery and the black to the negative side. A typical 12-volt deep cycle house battery should read approximately 12.4–12.6 volts.

A multi-meter can also be used to check the charging system of the RV electrical distribution center and its power converter or battery charger. Once again, place the red lead on the positive and black lead on the negative. Plug the shoreline power cord into a 120-volt receptacle and you will find the system may provide up to 14.5 volts of charging power.

This can also be done by starting the generator if it’s connected to the distribution center either with a j-box or manual plug in or an automatic transfer switch known as an ATS. During this procedure, you should see the normal 12.5 volts climb to approximately 14.4 volts or more.

Some units will provide a charge to the house batteries while driving down the road via the engine alternator. Motorhomes with this feature will have a momentary switch while travel trailers will connect using the 7-pin connector on the pigtail to the tow vehicle.

While connected, start the engine of the motorhome or tow vehicle and using the multi-meter, you will be able to verify a charge coming to the house batteries.

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14 Responses to “RV Battery Maintenance: Checking Battery Charge”

  1. Ken Johnston

    Thanx for the informative video. I have a 2000 Gulfstream Tourmaster powered by an M11 series 450 HP Cummins, a Cummins/Onan 7.5 kw genset, a house battery system powered by 4 6 volt 230 amp hour batteries and a chassis 12 V starter battery system. I have several questions about how to evaluate features of the integrated system
    My first question emanates from the fact that I don’t yet know which battery system powers my genset starter. (only bought this rig a few months ago) I have an AUX START rocker switch at the driver control panel. I understand it will power a depleted Cummins start battery using a charged house battery system. However, what if my house batteries power my genset and they become discharged? Can I start my genset with the AUX START switch? i.e. does the parallel switch work in both directions or is the electricity flow limited to one direction only? How can I test this?
    My second question is about the engine alternator’s function. Does it charge just the start battery or does it charge the start battery first and then, if the start battery is fully charged, share power with the house batteries as well? How could I test that, please?
    Finally, is there any thing the charger system does to handle generator input differently than shore power, or is the AC input from the genset distributed the same as the shore power input. Thanx in advance for your response.

    Reply
    • Customer Service

      Ken,

      Typically it is the house batteries that start the generator. There are a few manufactures that set it up differently or things could have been changed by a previous owner. When the generator is running it should be charging the battery that started it. It has a built in 12 DC charger so as it is running, the batteries will be getting charged. If the house batteries were dead, you should be able to use the rocker switch to connect the separate systems together to be able to start the generator and it will then charge the drained batteries as it is running. The electricity will flow each way, it is not directional. The best way to test this is to have the generator running or have the shore cord plugged into an outlet. Both of these systems charge the battery, you can check the voltage at both sets of batteries and if they are both getting a charge then they are connected through the switch. Typically only the house batteries get a charge when plugged in so if both are getting a charge, the switch is connecting them. As for the alternator, it should charge both chassis and house batteries when the engine is running. Since both systems are usually isolated from each other, there is usually a solenoid switch that connects the batteries when the engine is running. It is usually a can in the engine compartment. It has one wire to the chassis battery, one to the house set and then on connected to the ignition switch. When the ignition is turned on, the solenoid closes the valve and connects the two systems so they both get a charge at the same time. One doesn’t have to be full before the other, they both get the same charge rate at the same time. To test this, you want to start the engine and then test the voltage at each system and make sure they are getting a charge. Usually above 13.6 volts. As for your last question, the input from the generator is distributed the same as shore power. Usually there is a transfer switch that selects either shore or genset, it will only allow one at a time. With either one selected, it then sends the voltage to the distribution center. There are some older systems that might only allow the input to certain circuits but these are usually found on older systems. This is usually found when the generator is a low watt and can’t handle the entire system. Typically a 5500w generator can handle a 50 amp service on the lower end and 3500w would be fine for a 30 amp system. I hope this info was helpful!

      Sincerely,

      Dan
      RV Repair Club Technical Expert

      Reply
  2. Ken Johnston

    Hi folks. Please check your video at the 1:34 mark. I think an edit may be in order.
    Cheers! .. Ken

    Reply
    • Customer Service

      Dear Ken,

      Thank you for your feedback! It’s much appreciated and we’ll forward on the message!

      Please reach out if you have any other questions or concerns!

      Sincerely,

      Jessica
      RV Repair Club Video Membership

      Reply
  4. James

    I have a 08 Winnebago vista and am having the same problem. Not charging batteries even while plugged in, gen set also wont run. Could this be the same issue, inverter problem?

    Reply
    • Customer Service

      Hi James. I would start by checking the charging system of your converter or inverter. If you have the larger Freedom 2000 or similar inverter, it is also the charger, however if you do not, your distribution center will have a converter that should charge the house batteries. Start by plugging into a 30 amp source to make sure you have enough power, if you are plugged into a residential source that is 15 amp or even less and using the refrigerator and roof air conditioner, there is not enough power to also charge the batteries. You can use a 15 amp plug if you turn everything else off so just the converter is running. Next, take a multi-meter and check your charge voltage just like the video shows. If you are not getting a charge, then you probably have a defective converter. If you have an inverter and not getting a charge, check your owner’s manual as some have a fuse or even need to be “jump started” if the batteries were allowed to discharge.
      Thanks
      Dave-RVRC

      Reply
  5. Joseph

    my house batteries are not charging from engine or shore power – 2004 windsport 32R can’t find wireing diagrams so I can troubleshoot – any ideas

    Reply
    • Customer Service Techs

      Hi Joseph. I was able to contact tech support at Thor regarding your battery charging issue and that model utilized a “Battery Control Center” designed by Intellitec mounted inside the front compartment. It’s a 12”x 12” box labeled Intellitec Battery Control. Inside the box is a series of 5 amp automotive style fuses and a black test button. Check these fuses and the test/reset button. If this still does not provide a charge, you may need to replace the control, however they recommend contacting Thor directly. Tom Overton is in Technical Service and can help walk you through the process and possibly find wiring diagrams. He indicated there wasn’t a lot of documentation around that time as it was in transition from the former company to Thor. He can reached directly at:
      Tom Overton – Thor Industries
      877-855-2867 x 2079

      Hope this helps!

      Reply
    • Customer Service Techs

      Thanks for visiting the RV Repair Club site and the opportunity to assist with your battery charging issue. When you state “my house batteries are not charging from engine or shore power”, I would like to find out how you came to that conclusion? Not a challenging question, just starting with the basic troubleshooting 101 steps. To verify there is no charge coming to the batteries, first test the charge at the house batteries with a multimeter starting with the unit unplugged to test the current state of charge on the batteries, then plug the unit into an outside electrical source or turn on the genset and see if the charge changes. If there is no charge, or slight charge, check the converter to make sure the circuit breaker is not tripped. I would also shut off all other appliances such as the AC units, on the circuit panel to isolate the converter. Sometimes these appliances draw to much power and there is little left to charge the batteries! I remember in 1987 working at Winnebago we had a model with so many “Whiz Bang” electrical contraptions that when you were plugged into 30 amp shore power there wasn’t enough power left for the converter and the batteries would drain in about 8 hours even though it was plugged in! That’s about the time 50 amp power became popular!

      Next, use the same multimeter to check the power coming from the engine alternator. Placing the red on positive, and black on negative, start the engine and verify the charge. If there is no charge, you may have an issue with a momentary switch, a solenoid designed to allow a charge from the alternator and a jump from the house batteries to the engine battery by a switch usually located on the dash. Use your multimeter on the alternator side of this switch to verify a charge from the engine alternator. I would then recommend getting your batteries check with a digital load test.

      And finally, if you have an inverter that is part of the charging system such as a Xantrex model which was a popular item in the Thor lineup, check your owner’s manual for the reset procedure. Some of these models had a complicated reset method if the batteries went dead which required jumping terminals and such. I don’t remember the exact procedure, but it was a real pain for owners. Check your owner’s manual or the Xantrex manual if you still have it. Otherwise, get the model number and contact Thor or Xantrex and they should be able to get you wiring diagrams and possibly an owner relations rep that can walk you through it.

      Oh…one last thing…check the battery disconnect. I’ve been guilty of that one myself!

      Reply
      • Mark A Christman

        I’ve got a 2006 Adventurer pickup camper and the battery’s only half charge whether on 110 or connected to the pickup.

        Reply
        • Customer Service

          Hello Mark!

          That’s a great question!

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          Reply
  6. Edwin W

    Liked the brief summary but would like to have seen more info as to what is causing the house batteries not to charge when the engine is running. It gets expensive when you take your rig to a repair shop that has hourly rates of ove $100.00 per hour. Like to try and repair myself if knew where to start looking for problem.

    Reply

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