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Battery interconnect

Jim Corey

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If I run a wire from my house battery bank (which is charged from shore power with my smart charger) to my chassis battery (which is not), will the chassis charge be maintained while parked? Do I need a diode to prevent backflow? I have several items that are on the chassis battery, mainly electronic device chargers, that create a drain while parked.

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1 hour ago, Jim Corey said:

If I run a wire from my house battery bank (which is charged from shore power with my smart charger) to my chassis battery (which is not), will the chassis charge be maintained while parked? Do I need a diode to prevent backflow?


Jim, good questions, FWIW here are my thoughts.

 1) Sure, it’s possible and it can be made to  “work” to have your smart charger supply “some degree” of charging amps to the engine battery…………HOWEVER the amount of charge it receives depends on the connecting cables,  their size, distance and wiring configuration.

2) Sure, I would want a means to isolate the two to prevent any backfeed or discharges etc., however a Diode (a PN junction) has a 0.6 voltage drop and I prefer a quality  mechanical isolation relay instead.

HOWEVER THAT BEING SAID as a 47 year continuous RV owner, past dealer and Electrical Engineer, ITS NOT SOMETHING I WOULD DO.  

3) When charging multiple batteries in parallel, I prefer they be identical in type and size and design and age, which a deep cycle and a distance away starting battery ARE NOT. If that's what you have?? AGM or Lead Acid?? Deep Cycles for the house and starting battery for the engine I assume???  IE not a matched system

4) I prefer my smart charger be dedicated to supplying a full, complete, and quality charge ONLY to my house batteries and NOT mix it and labor it down trying to also charge some non identical distant engine starting battery. Even if it will “work” it may hamper the ability to supply that smart quality charge to the house battery bank.      

5) What I WOULD DO is use a quality Battery Tender, Battery Maintainer or what else called when plugged to shore power to charge ONLY the engine battery and NOT tie it to your quality smart charging system

6) Of course, I have often allowed my engine alternator to connect to my house battery bank via an isolation relay to charge them some while driving, but they DO NOT receive the full and complete and quality of a charge as my smart charger can provide. Again the connecting cables size, distance, and configuration determines just how much charge they may receive when driving

 Do as you please, sure it can be made to work, and just because it’s NOT how I would do it doesn’t mean you need to do the same, it’s your RV your money your choice.


 John T



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5 hours ago, Ranger Smith said:

Get yourself a trikl-start for $49.95. It will do all that for you

That is a much better idea than what you are thinking of. If you do what you suggest, by all means, do add a blocking diode but that is a very poor way to keep your battery. When we were fulltime, I used a battery minder on our chassis battery and mounted it in the area next to the battery, keeping it connected to the battery and wiring the power to be energized whenever the shore power was connected. I used the same starting battery for 7 years that way. 

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I used to do what you are contemplating and it did work.  I originally started connecting the HDT batteries to the RV batteries to use the RV solar to keep the HDT batteries up.  The HDT batteries only had the normal draw of a parked vehicle.  It still worked when we had power to the converter.  Due to the potential problems described by others, I added a 30 watt solar panel for the truck.  That keeps the truck battery charged and we don't worry about it.

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I've connected primary and secondary batteries with a VSR  (voltage sensing relay) with the batteries lasting for years.

On of my learning lesson was buying a battery minder that had a continual output that was too high for the battery I connected to.










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