Battery keeps dying... Please help!

[swc920526]

Hello guys! I'm new to the biking forum and this is the first place I've ever made an account with. I've seen a lot of interesting things on here and it really intrigued me. Haha. But I'm coming to you guys to see if you guys can help me with a problem that I am having with my bike... I own a 1996 Yamaha XJ600S. I bought the bike early last summer for around $900. It was riding all good and stuff and the engine seemed to be pretty strong but I kept having issues with my battery. When I first bought it the guy said that I will need a new battery soon so after riding it for a couple weeks, I went out and bought a new battery. When I charged it, it worked for a couple times but after the first few times the bike wouldn't start when I turned it off. I would have to either recharge the battery or jump the bike everytime. I then figured maybe it was the battery. So I went out and bought another one and did everything that was needed to be done and put it on the bike and it still did the same thing. I talked to one of my friends and they told me that I could have something that's running while the bike is off. I then went to my bike to see if something was on when the key wasn't in and it didn't seem like anything was on... I didn't know what it could be so I did some research on it and my best guess was that maybe it's the rectifier on the bike. I saw a few videos on rectifiers and how they will drain your battery even if it's not running. If it is the rectifier, how will I be able to check to make sure that, that's it? And if you don't think it's the rectifier, what do you think it would be? Because I'm totally clueless on what it could be. I'm not really that big of a electrical guy, I've done my share of changing stereos in cars or putting in subs in cars but other than that I don't know much about how wiring works or anything. Haha. If you could help me out I would GREATLY appreciate it!