The key here is make sure the replacement battery fits exactly, with the terminals and wiring laying as they were. In the case of my Sporty, many aftermarket batteries do not have an exact replacement. So before you substitute make sure it fits and meets the CCA rating of the HD OEM battery.
BTW, as Smitty says the HD OEM battery is very good and if you maintain it with a good battery tender, you should be good for at least 7-9 years before needing a change...pretty hard to beat that!