I found that "warranty" at their US sub-site, not at the german equivalent.
Furthermore they state at the warranty that it is about defects, whereas at both sites they indicate that their batteries may leak.
A recent test from a german consumer organisation indeed showed differences between the chances of used batteries to leak. The most cheapest, the ones I use, are most prone to leakage. (Which means I should either only install them where they are typically not drained at all, or where they are drained till exhaustion resp. could be taken out after use wihout hassle.)