we use this relay in or dual battery setups in our opinion its better than the "starter" relay's most of the other companies use...
a few specs on it:
Allows temporary isolation of house loads from engine circuit during engine cranking to protect sensitive electronics
Automatically combines battery banks during the charging cycle and isolates under discharge
12/24 Volt auto ranging voltage input
Waterproof rated IP67 - temporary immersion for 30 minutes
Remote LED output indicates relay state away from ACR
LED light indicates when batteries are combined
LED blinks in under voltage lockout and starting lockout
Supports high-output alternators up to 120 Amperes
Included with the ADD A BATTERY Dual Circuit System
Automatically combines battery banks during the charging cycle and isolates under discharge
Activates from any charging source - alternators, battery chargers, or solar panels
Hermetically sealed contacts / vapor proof
Side and bottom knockouts for power cable connections
Clip-on cover protects and insulates terminal connections
Tin-plated copper studs for maximum corrosion resistance
7/8" (22.22mm) stud length to accept multiple cable terminals
1/4" x 0.031" male quick connect terminals for ground and remote LED and starting interrupt