On 7/19/07, Dennis Haynes <d23haynes57@hotmail.com> wrote:
>
> The sure power isolator or smart relay is actually a voltage controlled
> relay. It connects the two battery banks when either one is being charged.
> When the charge source stops and the voltage returns to a battery only
> state, the banks are again isolated.

In addition the Surpower 1315 gives priority to the starting battery,
charges it first before charging the aux battery.  But it can be wired to
use the aux battery  in parallel with the starting battery either
automatically or with a switch added to the circuit.