spark and no spark

Some really great information above. My concern is the uni-body is not designed for starter current. Steel has about ten times the resistance of copper, for same cross section. The engine and battery ground straps add about double resistance compared the stock location, then add the great length, and poor conductivity of steel uni-body. The lower the voltage the starter sees, the higher the current it pulls to meet the load demand.
Running a large conductor copper battery to engine ground cable may be necessary.

And as others suggest the battery is sick. Any battery reaching about 11V without load is in the danger zone for loss of capacity, due to deep discharge.