2001 GMC Sierra DEAD batterie

I have a 2001 GMC truck !500 . the batterie has been changed twice . the one in the truck is only 90 days old . i ran a test on it it's good . the alternater is produceing 14-14.5 volts. but if the truck sits for 4-more days the truck will not start. the windows and door locks are NOT eletical , nor are the seats . The day time running lights have never workd , the head lights come one when the truck is started in the daytime . DEAD batter.


help ! ! ! ! ! !