The NEW SC80 offers many advantages not found with other brands of isolators, but the single largest advantage to having an SC80 in a dual battery set up, is the speed with which used battery capacity is replaced.
Because of the way the SC80 operates, by keeping all batteries connected after the ignition is turned off, and sharing 12v accessories power requirements over both the auxiliary battery and the cranking battery, if you use the same amount of battery capacity that ordinary dual battery system uses, which only use a single auxiliary battery, the batteries in an SC80 up set will only be discharged to half the depth you would have to discharge a battery in a single auxiliary battery type setup, as used in ordinary dual battery systems ( including DC to DC type Dual Battery Systems ).
SC80 SHARED Mode Cut-In ( Turn ON ) at 13.2v, Cut-Out ( Turn OFF ) at 12.0v.
By Cutting Out at 12.0v, the cranking battery is still left with 50% of it's capacity, which is more than enough to start the most stubborn motor on the coldest morning and as the SC80 is used in countries all over the world, including many up in the Arctic Circle, this unique operation has been well and truly proven as being reliable in all types of situations.
NOTE, the CCA rating of a battery is maitained in a battery until it is discharged below 40%, at 0C. So the SC80 will always leave your Cranking Battery in a safe state of charge.