Very little plastic needs removing to get the tank off a K100RT. If memory serves, you only need to remove the left lower fairing panel, and then only so you can get to the fuel lines and electrical connetctions. A single 10mm bolt at the rear secures the tank. Remove that bolt and pull the tank rearward.
If you do go the direct-battery route, don't forget a fuse holder in-line on the positive side!