1990 5.0 Mustang battery problems

I have a 1990 5.0L Mustang LX. The car sits for a few days, and dies. I have to keep jump starting it. When I jump it, it starts immediately. It seems as if it's draining just enough to not start. I have lights and all other electric, and I can hear the starter turning, but it's mostly just making noises. I have an Optima battery. The car used to sit for 2 weeks at a time (not that I try to let it sit that long) and it used to start with no problem. Now after just a couple of days, it won't start. Any suggestions??

I have a 1990 5.0L Mustang LX. The car sits for a few days, and dies. I have to keep jump starting it. When I jump it, it starts immediately. It seems as if it's draining just enough to not start. I have lights and all other electric, and I can hear the starter turning, but it's mostly just making noises. I have an Optima battery. The car used to sit for 2 weeks at a time (not that I try to let it sit that long) and it used to start with no problem. Now after just a couple of days, it won't start. Any suggestions??

Check to see if the alternator is in-fact charging, if yes, Check for short to power.