Just out of curiosity what are "good" battery voltage readings across the posts? I used a digital MM and the charge on a 24-36 hour not driven car was 12.25V, 12.45-12.46 right after driving it and 14.03V while running.

 

Technically, the fully charges rest voltage should be 12.6v fully charged. The car's charging system is designed for 14.5v plus or minus a couple tenths while running. After burning off the surface charge by turning the lights on or cranking it a few revolutions without starting the voltage should still be above 12.0v. Anything less indicates a failing battery.

Both your running and rest voltage seems low. Most auto parts stores will do a free battery/charging system check.