[Water Warrior 2]

Could be that the starter itself needs some TLC. If it is dirty and corroded inside it may need to be disassembled and cleaned up a bunch. The GZ has a smaller battery that can not overcome the dirty condition and still provide enough power to fire the ignition. Using a larger battery to boost the bike is a good way to fry a dragging starter.
Seen this in the past with cages. Dragging starter and a no start condition. Dead of winter and no place to plug in the block heater. The cage was power boosted with 24 volts finally and the starter went up in smoke. Me: outside at 40 below changing starter. New starter and battery charged up. Engine started first try.