There is a lot to this battery business. The manufacturers have got it down to a science as far as longevity. Price may not be an indicator of the quality.
There are a number of variables that will affect the lifetime. Number of discharge cycles, time spent dormant at what temperatures, whether or not partially or fully charged. Batteries that are used in our cars are referred to as SLI service. Starting, Lights, Ignition. High Amperage output, not great for slower discharge rates or cycles. The opposite would be a deep cycle battery that is designed to be fully discharged at a relatively slower rate, and not as capable of providing the high amperage we need to start a hot Cadillac V-8. Battery design gets involved, and manufacturers are combining elements of both in batteries now.
My truck tractor has 4 group 31 batteries, with a CCA(cold cranking Amperage) of 1050 each. Regular flooded cell batteries in this service lasted me about 18 months. I am trying a set of AGM(absorbed glass mat) batteries now, hoping to get 3 years out of them, seeing as they cost twice as much.
One of the bigger manufacturers is near me, East Penn Manufacturing near Kutztown PA still has a genuine factory outlet where you can buy anything they make, in 1st or 2nd(blems) quality.
Website has lots of info about batteries:
http://www.dekabatteries.com/