Cheers Glen
Thing is I am usually not there the next day to supervise as my observatory is on a friends property ie I don't live there (no mains power). So I wanted to be able to just connect the seperate smaller battery to the big bank when I leave and be confident that if I am not back for a week or two I don't ruin the system or worse, melt or burn down the shed
The smaller battery is almost certainly likely to have less charge then the big bank when I connect them. I was thinking it was probably not really an issue but given the smaller battery is not an AGM style battery like the big ones and it's older plus the ideal charging specs of the two different batteries may be an issue too ie the big batteries need to be bulk sharged at 14.6V and thisi may not be good for the smaller battery..? So I was worried there may be some issue connecting them hence why I was thinking the DC to DC charger...?
Yes my solar regulator is also 30A and no the load is not running of the regulator but connected straight to the batteries via the inverter, I think the regulator manual said a fuse wasn't really necessary..?
Mike