PHAZE,
The secret to long life with a lead-acid battery is never letting it sit in a discharged state, which leads to sulfation and permanent loss of capacity. As many others have said, keep a Battery Tender hooked up anytime you won't be riding for more than just a few days. I've had batteries last as much as 6 years doing this, but I agree with the others that it would be best to replace it before that. I just think 2 or 3 years is too soon, 4 years is closer to the sweet spot for a modern lead-acid battery that is maintained properly.
There is a lot of confusion about "gel" batteries, with many people using that term for any sealed battery. A true "gel" battery has the electrolyte "jellied" by adding a silica material until it becomes a thick paste. This makes for a battery that can be used in any position and that won't leak if broken open. This type of battery can be found in things like laptops and portable power tools, but is rarely found in motor vehicles. They typically have less capacity than the same physical size AGM or standard battery, and require specialized charging systems for optimum performance.
Another type of sealed battery is AGM, or Absorbed Glass Mat. This type uses just enough liquid electrolyte to keep the fiberglass mats wet, and there is no excess liquid so this type also doesn't leak if the case is broken. The AGM type is what comes stock on your Harley.
The best bet is to stay with the AGM type battery. Your bikes charging system was optimized for that type of battery, and the AGM provides the same leak free, multiposition advantages as the "gel" battery at a lower cost.
Jerry