I have posted on other threads here but cannot fid where. You cannot use a true gel battery in a Rocket without making changes in the regulator. Gel batterys charge a a lesser voltage and will be short lived with the standard regulator. AGM batteries (Absorbed Glass Mat) like the OEM battery in your rock are the best without major changes. To make them last longer use the Electronic "Smart Chargers" to top off your battery at least once a mounth. Even if you are riding an a regular basis. Smart Chargers will not overcharge or harm your battery. i have a couple of these chargers and have something on charge most of the time. I routinely get 6 to 7 years life out of each. (not including cell phone batteries they are a pain in the ars)
Battery tender says you should keep it hooked up all the time. I worry about it failing and burning down my house.