Fatcobra

I have swapped the motor 2 years ago and i have change the alternator and battery about 2 times after a couple of months it will not stay charged. I don't know what to think is the issue. I really don't have the time to fix it but i am going to have to make the time. I can start the car up and it will stay on but as soon as i turn it off it won't start again. I do have an audio system and a monster tach. Would anyone have any ideas on what could be the issue?