A deep cycle battery is a battery that is designed to produce steady power output over an extended period of time, discharging the battery significantly, at which point it must be recharged to complete the cycle.
The level of discharge is the “deep cycle” and stands in contrast to other types of batteries that provide only short bursts of energy before they need to be recharged. To be specific, a starter battery discharges only a tiny percentage -- usually 2 to 5% -- each time it is used.
It can mostly last up to six (6) years with proper care and charging, but also will depend on the frequency of use. It's up to you to make sure that your battery isn't being damaged by your charging routine.