The characteristics of the two:
Deep-cycle battery is capable of smaller peak currents, prolonged current draw and constant charging. You can also discharge it until it's dead and recharge with no problems. They're typically used in recreational vehicles and for trolling motors on boats.
A starting battery is capable of two or three times the heavy peak current you'd get from a deep-cycle battery, required for turning over winter-cold engine -- hundreds of amps of current. If you deep-discharge them until they are dead before recharging, they will have a short life expectancy. They're more designed for brief, high-current draws and that's all.
Dean