Use to swtich between battery banks.  Just require 1 solenoid and 1 switch.  When you turn the switch on it will switch from bank 1 to bank 2.  Much simpler solution than using 2 relays.

Heavy duty solenoid. 1 pair normally open, 1 pair normally closed, which reverse when activated.

Specification: 
100amp continuous, 
300amp peak. 
4x8mm studs. 
2x5mm studs. 
Mounting bracket 60mm centres.