Rv dual 12v battery system

I have a 75 watt Siemens panel and Morningstar PS-20M controller in my RV. I use a Perko Switch to sellect each battery or combine both and use the off position when in storage. I have been using A West Marine C150 Battery combiner between the 12V batteries to keep both charged with the output of the charge controller connected to one battery. The equipment is about 10 years old and has worked fine until the recent failure of the C150. When looking for a C150 replacment I have found that Morningstar now offers a dual battery controller , SSD-25RM, that looks ideal for RV use. Does anyone have a suggestion for a C150 replacement or would it best to upgrade to a dual battery controler.


  • System2System2 Posts: 6,290 admin
    Re: Rv dual 12v battery system

    here is what I did in my Suburban truck: I have two Optima Yellow Tops and wanted one to be a truck battery and another 'toys' (stereo and a 2000W DC inverter). I bought a SurePower 130amp isolator (with a trigger lug. Thus four lugs total: one for each + terminal on the battery, one from the alternator (130A HD bosch), and a trigger lug - wired to the ignition wire) and have separated two loads completely. Since Ground is Common, I added a 4ga cable between two positive lugs of the batteries and mounted a simple DC On/Off switch - thus if I ever need to combine the load/batts, I just turn it right (close). Has been rock solid setup for 6 years (I do go through Optima's every 3 years, thus those have been replaced - thanks goodness for a Johnson Controls employee discount and cost delivered at sub $70 per battery (1/3 of the retail cost)). hope it helps.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Rv dual 12v battery system

    I have been convinced by the tech section at SmartGuage to stay away from diode-type isolators:


    For alternator charging my old 1976 camper van has a "split-charge relay", which is just a relay that connects the two batteries together whenever there is alternator current present. I was originally concerned about high current from one battery to the other, until I read this:


    To the OP:

    The SS-Duo should work fine for you, but with a single 75w panel you could probably get by with the 10 amp unit instead of the 25a. The only issue is that there is only one battery temp sensor connection, but there appears to *also* be an internal temp sensor - so the prevailing wisdom (actually...WAG) is to install the unit next to one battery (say the house battery) and use the remote sensor to monitor the other battery (say the engine battery).
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