i have a 2001 mustang gt that wont start,but if i put a battery charger
on untill it shows full charge,it will start.it has a new battery that test
with flting colors,and car wont start,i test battery with volt meter
and it says 12.6 volts,but if i hook up the battery charger it shows
the battery is almost dead,but if i charge to where the charger says
full charge,the car will start. any help out there?

 

sounds like a bad battery. when you get it running check voltage at battery, should be 13V+

 

Sounds like a battery problem pull it and have a shop test it or if it older then 4 years just buy a new one