How long a battery lasts depends in part on how often and how deeply it is discharged. It is also important that the battery is charged properly and with the right battery charger. With normal use (i.e. the battery is not often discharged and charged), a service life of 5-8 years is feasible for the Gel battery and AGM battery. When using 2 Volt NiCd cells, a service life of 10-15 years can be achieved. When the batteries are frequently discharged, the service life of the batteries is reduced.
It is also important to consider the ambient temperature. A normal ambient temperature is 20°C, when this gets higher it comes at the expense of battery life.