2002 Mitsubishi Mirage help?

I drive a 2002 Mitsubishi Mirage. About a month ago I was driving home from work, and I noticed my radio was cutting on an off. I didn't think anything of it, just maybe my CD was messed up. So as I got closer to my house, my car started shuttering, and not wanting to go. When I got home, I tried to crank it, I heard a popping noise, and it wouldn't turn over.

So initally, I thought my battery was dead. So I got a jump, and it started, then died moments later. We tested my alternator. It was only putting out 7 volts of power. So I went and bought a new alternator, and I was excited to get it running. Driving about 10 minutes later, it died. So I had my friend come over, and test it. Alas, only 7 volts of power. So we charged my battery, and I drove home.

This alternator isn't bad, it's brand new, and the third one to do this. So I ask, what could be the problem? The battery is new, and ran off the new battery until it died. So the alternator isn't charging. Could it be a bad ground, and if so, i'm guessing to replace them?