Grease,

 

Your battery needs a load test - there may not be enough ummppf left in it.  Also, check battery connections, including master and starter relay, and engine ground connection.

 

Even a little resistance from a bad connection can cause a large voltage drop (Ohm's Law) at high amperage, like during start.  B&C will tell you that SkyTech starters place even greater demand on the battery at lower voltages because of the way they are wound.

 

After years of screwing around, I have had great success with my final configuration of B&C battery, voltage regulator, alternator and starter.