So it turned out that the battery price is 18.48 euro, but the "repair" (trivial replacemenet of battery which takes about 25 seconds) costs 18 euro, so together it is 36.48 euro.
For the whole picture i am adding that this is happening in Slovakia (EU) and the company
http://esc.sk was recommended to me directly by Pocketbook representative. /off topic: minimum hourly wage in Slovakia is currently 1.99euro brutto./
I refused to pay 18 ridiculous euro for battery replacement. Also this whole case made change my mind about Pocketbook, i will not buy from them again.