1996 Ford Contour GL exterior/electrical Issues?

I recently bought a 1996 ford contour GL from my buddy for 300 bucks. Yes it's a cheap car with 175thou miles on it but it's what I can afford. It starts great, runs good, after I bought a new valve cover gasket anyway. Well my EXTERIOR problem is that the door that goes over the gas cap, the thing that holds it shut broke off. I've tried velcro but it just comes off, any suggestions? My elec issue is that. The battery would run down over night unless I took the batt cable off, no lights were on or nothing. So I figured the battery might be gone, I took it tested and it passed great. I put a new alternator in. Same issue. I put a different battery in, worked great for about a week, now it does it off and on. Anyone having the same problem? Begging to be very aggravating, hoping it's fixable! Thank you all! ANY suggestions are welcome.