To electrically heat springs to revert to original length: Alkaline batteries offer the safest method of electrical heating. Two “D” size batteries in series give a supply voltage of 3v and a current of up to 3A when the batteries are in good condition. The smart spring alloy itself has a low electrical resistance. However, its surface has a high electrical resistance and also will not permit soldering. The best way of connecting a spring to battery leads is by small screw connectors cut from multi-way connecting/terminal blocks. Using pliers, bend about 8mm of spring material at both ends parallel to the springs main axis and screw these into the connectors alongside the connecting wires. Additional wire(s) in the connectors can also be used to link the ends of the spring to whatever the spring is meant to move or actuate.