Thanks for both those replies. That Intervolt system looks like it might be the best for me as it has a higher current rating, so will find out a price. The Invertek system looks good in its own right too.
I can't find out if this suits AGM battery setting., if the cranking battery is flooded wet and house is AGM.?.
The alternator see the flooded wet @ 13.7v. not the AGM with the 20 year old existing unit.
Unless you really want to use the VSR to parallel your house and start batteries for some reason a DC to DC battery charging system is becoming a better solution for dual battery systems and charging the house batteries faster and correctly.
Link: http://www.cteknz.co.nz/tabid/319/Categ ... fault.aspx