Battery cable lug fracture are a known problem on the UCEs- many of us, including myself, have experienced this first-hand. I chalked it up to a bad batch of lugs, but today I've seen the error of my ways.
I put a new gel battery and Battery Tender cable on my B5 about 3 months ago. Today, I tried hooking up my Battery Tender to my previously installed cable, but I wasn't getting a charge.
I took off my battery cover and what do I see? A broken negative battery cable lug, off of the Battery Tender cable. I hit my friendly NAPA autoparts, bought some new lugs, replaced the old ones, reinstalled everything, and now it works perfectly.
After today, I'm going with metal stress from motorcycle vibration, as opposed to manufacturing defect. RE, you have been absolved.