Likely you have the "Button Fob" if you have Security system, but if it is "Buttonless" you will have to turn on the ignition switch, then pull the main fuse...otherwise the automatic arming will slam your ears with 120 dB horn blaring, because it thinks someone is "tampering" with the battery.
This is why it is a good idea to have a service manual before doing any service so you don't have any surprises. May not surprise you, but if your hands are in a tight place or near sharp edges, you could hurt yourself by reflex response. When disconnecting the battery follow Jacks' advice, and yes HD battery is great, Deka is fine...but for my Sporty, the HD one is the only one that fits in the tight space made for it...hardly any room for even the Battery Tender harness...so I just "bite the bullet"!