The price difference between local local shops and online trading in specialty batteries rarely purchased is often partially 5-, 6- or even 700%. Therefore, the decision for the double pack of Duracell had fallen relatively quickly. With prospective buyers for the purchase directly from Amazon and the consideration original packaged goods with (hopefully) sufficient durability was to get (was here earlier in the reviews of problems read the reference on MarketPlace dealer: "loose in an envelope with an expired shelf life"). The batteries purchased directly from Amazon were boxed and have a shelf life "Best Before 2017" specified.
The class name of the so-called "3A-12V batteries": similar names of Duracellbezeichnung "MN21" of other manufacturers are: "A23 / K23A", "LRV08" or "V23GA" (Varta).
Conclusion In the case of the cover via Amazon recommended because: cheap, boxed and with sufficient durability (2017).