Small Engines (Lawn Mowers, etc.): Noma 20hp B&S Wont start w/o a jump, battery cables, negative cable

Question
I have a Noma riding tractor, 42" deck, that has a 20hp B&S engine.  I bought it second hand last Fall and it ran well.  I used it throughout the winter to plow my drive and it began to act up.  It started to crank slower and slower while starting.  I started to have to put a charger on the battery before starting it, then jumping it to get it to kick over.  I had the battery tested and it was ok.  I changed the plugs and the oil.  Just yesterday I jumped it to mow my front yard, then I could not get it started without the jump for the back yard.  What else should I be checking?  The positive terminal on the battery was a little corroded, but I cleaned and brushed that up.  The wire looks a little worn at the connection but not too bad.  Is it possible the battery is undersized to crank the engine?  

Answer
Sometimes the cables will corrode inside the insulation causing the same problem.  More commonly this problem is caused by dirty battery cable ends and battery terminals.

Dis-connect the battery cables and clean the terminals and cable ends with a wire brush.  Also make sure the ground/negative cable end connected to the mower frame are clean.

Let me know what you find.
Eric