Batteries deteriorate over time, no matter how much or how little they are used and even if they are kept on a battery tender religiously, so it's a good idea to have your battery load tested to determine how much capacity has been lost over time. You can do as some recommend and just replace them every couple years, but that may mean wasting a lot of useful life and money. Or you could do as some others recommend and just assume yours will last six or more years, which usually results in walking out to the bike one day, usually when you have an important place to be, and the battery won't even turn the engine over once. This method leaves you at the mercy of the local dealer, who will be happy to charge you $180 plus tax and fees for a replacement, versus being able to plan your purchase ahead of time and get a much better price elsewhere.
I've used H-D batteries, and I've used Deka batteries of the same size that cost slightly more than half of the price of the H-D battery. Some of those H-D batteries were fine, one failed in two years. A higher price does not guarantee a better battery.
Jerry