bv;

1. Voltages measured under no load conditions are NOT informative as to what state of battery charge is! To make a determination on state of battery charge, you MUST make your voltage readings under worse case (starting) load. If voltage collapses under starting load, bat is either discharged OR has an internal problem such as a high internal resistance or dead cell.

2. A "good" battery in a good state of charge (one whose voltage stays up and does not collapse under starting load) will STILL not be able to start a vehicle if poor connections (external resistance) along the way causes a voltage drop at the load effectively giving it only part of the voltage available if the connection was without the resistance...

From the sound of symptoms, you have a poor connection in line with the starter (and this can be ANYWHERE in current path), which needs to be located and corrected. Locate by looking for voltage drops with you meter UNDER LOAD CONDITIONS! Once voltgae drop is located, recondition connection by cleaning and tightening. Use ACZP to prevent corrosion problems in future. See: http://sw-em.com/anti_corrosive_paste.htm

Just for gagas, perform a load test on bat to ascertain its condition...or have one performed at a service center that has a load tester...a device which puts a heavy load on bat and checks voltage at same time (sound familiar?). As chemical storage reserviors, lead acid bats are highly temperature dependent. Problems typically show up in winter when the extra they have is still not enough...

Good Hunting!