It's worth noting that some have found that the Opus has a few design flaws internally. When you get your Opus, open it up and check to make sure the Neg wire isn't running between to the terminals, or put something to make a spacer.
During normal use, this may not be a problem. But with the heavy use that we put these through, and cell testing back to back, the capacity testing can start to melt the wire coating that could potentially lead to a short.
Also, check the soldering connections to make sure they are all solid.
I can't remember who posted the original pics with the melted casing; maybe someone knows which thread it is and post a link to here.