It has to be cut off.
You don't remove the fender; the battery is behind the inner fender well behind the rear driver's-side tire.
which fender frontor rear front
Remove the driver's side rear wheel; remove the inner fender well behind the wheel.
Removing the rear fender from a 2007 Vulcan 900 is not hard at all. Simply remove any screws or fasteners and wiring that are holding the fender in place. There are tutorials for removing the fender online at YouTube.
with the motorcycle on the ground install tire change tool from tool kit across the tabs on the frame then put motorcycle on center stand. Remove rear fender bolts to raise rear fender, remove axle bolt then remove rear tire.
It's on the driver's side fender, a little bit behind to the rear of the overflow tank. There are two rectangular black boxes attached to the fender. They are covers for relays. It's under one of those.
You must remove the entire rear fender.
The procedure differs depending on the year and model, but basically you remove the wheel, disconnect any wiring and remove all fasteners holding the fender in place.
Remove rear calipers and pull. That simple.
A pound of C4 and a website with no actual answer.
eBay or CraigsList are your best bet.
The seat bolts are attached to the seat and extend from the seat to under the rear fender. Remove the two nuts under the rear fender that hold these bolts and lift up on the back of the seat. It is now free.