I've been looking at keeping the cab battery topped up with residual power from the recently installed solar setup. I have seen the VanBitz battery master, which I don't think is suitable as I don't want both batteries to go flat (there is a potential for that) and it is expensive, The CAK CSB2 looks good...but seems to do the same job as the Smartcom relay which is half the price or less. Both switch on at a certain voltage and off at a lower voltage. But the CSB2 limits the current drawn which may be the important bit as when starting the van a lot of current could be drawn through the relay and melt it. Has anyone any experience of the Smartcom in this application?