What you really need is a multimeter to check continuity and voltage. You can almost bet that your problem lies on either end of your battery. But looking at it won't tell you anything unless it is a fuse issue. Your Ground strap could be either loose, corroded or broken. Same thing could be a problem between your positive post on your battery and your converter. Without a means to test the lines, you can only guess. It is also possible that your new battery has a dead short in it. Again you need a meter and a working knowledge of how they work.