BFL13 wrote:
Two dissimilar batteries in parallel where one is 85AH and the other is 150AH will be at the same voltage. Their bank capacity is now 235AH.
When a load is put across the pair, each will be drawn down equally according to its proportion of AH size. Each will reach 50% SOC at the same time and their voltages will still be the same.
IE their voltage will be 12.2, and capacities now will be 42.5AH and 75AH.
So you can camp with these no problem. You can do 50-90 recharges with them connected no problem. Where you have a problem is charging them back to 100%
So at home you separate them and get each up to 100% by its own specs. Now you can put them back in parallel and float them at 13.2 or so and they will both stay fully charged.
You cannot put them back in parallel and just let them sit with no float voltage or else they will self-discharge with one battery eating the other and all that bad parallel stuff. You could leave them separated and just sitting there for a while--longer when it is cold out.
Time2roll has always said leaving them on a float will make up for all that because there is enough voltage to keep them both up even if they each want a different amount and there is some action going on between them.
as long as the batteries are similar construction and similar internal resistance your analogy makes sense. but a GC has much much higher internal resistance so when in parallel with a 12V marine battery unless the discharge and charge currents are reasonably low not sure the analysis holds. on discharge, the GC under even moderate load will have more internal voltage drop than the 12V causing the 12V to share more of the load and discharge faster, then having the GC charge the 12V when the load is removed.
but then I've never run a combo like this so I don't have any first hand experience.
