Currently have an Orion-Tr Smart 12/12 18A isolated DC/DC charger between the main and leisure batteries. Also a solar panel via a Smartsolar charge controller. Looking at installing the Ablemail AMT12-2 battery maintainer to trickle charge the main battery as the drain is substantial enough to cause a flat main battery in the winter (rather than use the plug-in charger). The DC/DC charger has 2 positive connection points and 2 negatives providing separation between both batteries. The battery maintainer has 2 positive connection points and 1 negative. Positive connectivity is straightforward, however, been advised to link the negatives together (obs using the same csa cable size as the battery cables) but then the DC/DC charger is no longer isolated. Measured 335 ohms across the DC/DC charger negatives. All threads that I can find are regarding non-insulated DC/DC chargers with the single common negative connection which I’d use. Is there any reason why the starter and leisure circuit negatives are isolated? Can the negatives be connected together at the DC/DC isolated charger without any detriment to safety? Any advice greatly appreciated please? Thanks