I do not know ...

,,, Late November bought such a 2-er Pack in order to use these in our smoke detectors. No sooner said than done and beginning December 2 weakening batteries replaced by this. Annoyingly, the beginning of last week reported the first and now the second smoke alarm due to low battery power. Annoying, after almost 3 months and amazing because the previous NoName batteries held almost 11 months.
The printed expiration date certifies March 2015 (03/2015), so we got no "old stock".
Well, now others will try.