Originally Posted by herk7769
This is totally true if the batteries are not matched.
The more "unalike" they are the worse it is.
For example an engine starting battery and a deep discharge (RV) battery wired in parallel would actually have LESS total capacity than the RV battery alone for the reason you stated.
The starting battery would always seem "dead" to the RV storage battery and it would keep trying to charge it.
Correctly matched RV batteries wired to make the resistances from the positive terminal of one battery through the stack to the negative terminal of the last battery IN the stack will prevent this. NOTE: The wires BETWEEN the batteries MUST be of the same gauge AND length for this to be true.
Herk this (just like the pic) is what I did,in a few weeks,I will let y'all know how it worked.
On a different note, today I will be wiring in my new transfer tank pump, I am trying to decide where to wire it to. Thinking about putting clips, like charging type,on end of the wire,and an other deep cycle batt,in a batt box,and charge as needed. Or I am wondering if I could wire it to a trailer plug,using brake pin as hot, The pump came with (I think) enough wire to go to one of the trucks batts.or the fuse box in engine compartment. What would you recommend ?