It's probably NOT your starter!
While starters DO fail, their failure rate is much lower than batteries, especially given that a car battery has a pretty definitive lifespan. Finding a battery that has lasted 5 years (in particular here in Florida) is fairly rare. About 4 years is a good average for a decent (not the low-end economy ones) battery. We get calls all the time that begin, "My car won't start; I think it's the starter because all my lights still work". Okay, just for starters (no pun intended) it takes a very small amount of juice to power those lights. By comparison, the amount of power required to spin the starter and crank the engine is IMMENSE!
Our next question?: "Does it go click-click-click when you turn the key" frequently brings a "yes" and we take an educated guess it's probably the battery. The noise is the starter solenoid attempting to engage, but being unable to function properly due to low voltage.
We also get, "My car won't start; I think it's the ALTERNATOR". No, it's probably not. Like your starter, alternators are generally reliable and last a long time; often for the life of the vehicle. The alternator's purpose is to recharge the battery after starting and to operate electrical systems when the engine is running. It has ZERO to do with actually cranking the engine; that is the job of the battery and starter.
If you've noticed that your car is cranking a little slower lately, it's a good idea to visit your favorite garage and have them run a quick test. Often the battery degradation is so slow over time that people often don't detect it until the day it won't crank when they turn the key.