Z5 premium battery

[filano]

Hi everybody, since a while I have had some battery problem whit my z5 premium. After getting some information about repair cost I have understood that it's much cheper to buy a battery and replace it by my self. But there's a little problem, someone suggested me that it's better to buy a battery which wasn't produced before two years ago, so I have to chek the production date, but, after a long reserch I wasn't able to find production date neither in the battery image nor in the product specifications. Can someone please tell me where I can find the production date for the specific battery model or, better post the site's link where I can buy an original battery not produced to much time ago? Thanks