Preview: Boat Wiring, Part 6 – The Two Battery System

30 Responses So Far to “Boat Wiring, Part 6 – The Two Battery System”

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  Tisha Lane says:

  Great Video! I have a boat and the batteries are located in the back end. The switch is mounted externally next to the motor. It would be so much more convenient to have the switch near the drivers seat!

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  Randy Walsh says:

  What battery suggestions do you have for a Cummings 4BT3.9?

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  William Nichols says:

  I have heard from a number of sources, that it is best to replace batteries all at once. If I have a two battery system and one is pretty good and the other is no good then I should buy two new batteries.

  This “rule of thumb” that batteries should be replaced all at once does not make sense given that one battery may be a starting battery and the other a deep cycle battery. Given that they are both fundamentally different types of batteries and will never really match each other why should buy and replace them together. One battery will probably fail will before the other. Why not just replace each individual battery when they independently stop functioning well?

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    Brent Ash says:

    Why not just swap the existing House battery for the Starting battery instead of replacing both?

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      Matthijs Siljee says:

      What you ask a house battery and a starting battery to do are different things: House batteries may have lighter loads, and the kind of discharge is different. The start or cranking battery needs to provide a great amount of current in a short time.
      You could substitute one battery for another in an emergency, to get you out of trouble. But for a longer life install the right type of battery for the right kind of task.

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  Lance Ryley says:

  I would have liked to have seen the back of the battery switch and the combiner without the cover on it, and perhaps a little more talk about how where the alternator or other charging source was connected for this boat.

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  Gary Freeburg says:

  I would like to convert my old four way switch, 1/both/2/off to the on/off/manual with the combiner that is in video 6. I have (2) 100 watt solar panels that are connected to the house bank that consists of (2) 6 volt golf cart style in series to make 12 volts. Would the combiner work in this case to charge all the batteries? If so, would it make any difference which battery bank the solar panels are connected to from the solar charge controller? The rated charge for the panels is 20 amps, is that enough to activate the combiner?
  I appreciate the videos.. thank you.

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  willem janssen says:

  Hello Don Eley,

  I own a motorsailer fisher 25. I saw the video part 6 about the two battery system. Is it possible to use this system with two different batteries?

  kind regards
  William Janssen

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  willem janssen says:

  Hello, I own a motorsailer fisher 25. I saw the video part 6 about the two battery system. Is it possible to use this system with two different batteries?

  kind regards
  William Janssen
  email: w.janssen36@chello.nl

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  Robert Smith says:

  On my project, I have 2 engines and 4 batteries. I get how to use the switch and the combiner for each motor and battery bank, basically 4 banks, but how would you connect the house batteries? It seems like from an output stand point, I should be looking at a 3 bank system. I would like to connect the 2 house batteries for the onboard electronics and leave the 2 cranking batteries isolated for starting the motors.

  Is there a way to use the method in the video for charging from the motors but still have the house load connected/combined to use 2 house batteries?

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  Allen Kennedy says:

  Thank you so very much for taking the time to put this series together and share with us. Tremendous help to my current 26′ center console restoration. I also plan to rewire the bilge pump on my 22′ sailboat per your method. Can’t describe how much I appreciate Mr. Eley and OCH for doing this.

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  john kelley says:

  Absolutely fabulous series.I could not have wished for more. You have answered a specific question which has troubled me for a long time.I have an old plank boat which leaks a lot. The bilge pumps keep the ^#!%^&^ thing afloat, ( bilge pumps are connected to the house batteries ) until one day the solar panels failed to keep both house batteries charged and the boat nearly went to the bottom with my brand new engine. Now I know I can connect the cranking battery to the house batteries via a connecter and obtain charge from the alternator as well as the solar panels which will help to keep the house batteries charged for much much longer. Thank you, thank you, thank you.

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  PETER RODMAN says:

  Very helpful set of videos! I have to repeat one or two questions, though: First, what type and size are the fuses on the lines to the battery combiner in the runabout system? And second, would you add fuses for the battery lines? If so, what size should they be? Thanks very much for the clear and thorough videos, and thanks in advance if someone at OCH can answer those two questions.

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  Mark Ritter says:

  I’ve gotten to the wiring on my Harry Bryan Rambler build. Thanks for taking the mystery out of the process. I’ve done a lot of automotive and home wiring, but this is quite different.

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  Joseph Helsley says:

  Great, high quality series on the basics! I’m not disappointed in the series at all, just would like to see an extended series on electrical systems for cruising yachts, something a little more sophisticated than simply trying to extrapolate from the basics here. Things like wiring a radar system, after-market boat lighting, water-makers, refrigeration, etc., and especially figuring up total voltage/amp needs, etc. I can just see the membership price going up now..:-)

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  Sean Rhone says:

  Loved the series but would love to see a simple setup done from scratch. Start with the battery, not wires run and nothing connected to the buses. Run the wires and say hook up a marine radio or maybe a VHF.

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  Francis Thomas says:

  Thanks video series was great.
  Just one question. I have pretty much the same set up with the switch and combiner and would like to know how many amps are the two fuses that were installed with your system.
  Thanks FT

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  Stephen Nesbitt says:

  I was about to build a system based on the two battery system described in the video. However, I read in Honda’s owner’s manual for the 9.9 HP engine that its alternator is intended to charge a starting type battery only, not a deep cycle battery. How do I deal with that type of situation? Their manual shows a single battery setup with wire to the accessories running off the starter battery.

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  Yurik Maria says:

  Thank you very much for these videos. I’m gonna do the wiring based on these videos.

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    Yurik Maria says:

    Today I tested the wiring system…everything is fine ! Thank you Don ! Thank you off center harbor !

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  Yurik Maria says:

  hello Don,
  On some diagrams I’ve seen circuit breakers between the battery and the battery switch. Is this a must ?

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  Linda Knapp says:

  Nice series. I would like to continue on to a more complicated system that includes Battery Charger, Solar/Generator, Engine and perhaps some good ways to wire separate areas. I am faced with rewiring a pilothouse cutter at the moment and looking at planning out the project.
  One tiny critique – I would love it if the camera was not constantly in motion. Focus on the center of interest and don’t zoom in and out while holding there.

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    bernard spenle says:

    Very clear and useful instructions. Thank you.
    I was wondering the same thing as the previous comment. Shouldn’t there be some charge regulator between the motor/generator and the batteries, to avoid overcharging?

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      Don Eley says:

      Bernard,
      Many alternators have a built in voltage regulator that maintains the battery at an appropriate voltage. This is why it is important to ensure you have the correct voltage regulator setting depending on the battery type: flooded, gel cel or AGM.
      If the alternator has an external regulator it operates on the same principle, sensing alternator voltage output which then controls charging amperage.

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  Brian Landry says:

  great videos, but how add to my panel if it is full? I want to add a am/fm radio, fish finder, sonic hub, down riggers, cigarette lighter adapter. I also have wires going directly to the battery, how can I clean that up, Can I buy a ground bus and power side all in one.

  Thanks again for some great videos It has given me more ideas.

  Brian

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  Gino Del guercio says:

  These are terrific. Let’s see more videos like these. More basics of marine systems. How about a series on rigging for cruising sailboats.

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  Pasi Kimpimaeki says:

  Will the relay work with different sizes of batteries? One “regular” size starter battery and D8 size 250 ah battery.

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    Don Eley says:

    Pasi,
    The relay shown in the video will work on different sized batteries. However what is important is the manufacturer and type of batteries. Flooded (wet cell), Gel cell and AGM batteries all have different charging voltage parameters, as do different manufacturers. If both the 8D and the smaller starting battery are all the same type the charge relay should work fine. You will need to make sure that the regulator on the alternator is also setup for the appropriate type of battery.

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      Pasi Kimpimaeki says:

      Thank you!

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  Robert House says:

  I am involved in the rewiring job on a 302 Ford motor in my 1974 Whitewater 22′ center console with a Hamilton Jet pump. Much of the wiring was removed and putting it back together has me stumped. Anyone willing to offer me assistance to a clean Coast Guard approved project boat?