Battery last 3 days dead after that - 1991 GMC Safari

With a multimeter test the voltage from alt to bat should be 14.2 volts test battery after a charge should be 12-13 volts not disconnect negative from battery and put your multimeter on fusable 10 amp and do a draw or drain test plug the black cable from the multimeter to the battery and the red cable from multimeter to the cable neg black on the car side cable unplugged from battery make sure keys are out of the ignition and the doors closed and nothing on in the car you should see .05 mv to .03 mv if you have more after a 30 mins test or 1 hour test then you have to find the drain on battery to find this you take out fuse at a time to see if it chages repeat not all the fuses at once 1 at a time