I have first bought this battery at a MarketPlace provider. When the battery arrived in a simple clear plastic bags, I was a little suspicious and asked Uncle Google, how it looks with counterfeit Samsung batteries. Compared with the original battery that was supplied with the S2, the color and the font of the print was in fact slightly different in this. On a forum I came across the suggestion to simply weigh the battery - and lo and behold: while the original battery with me about 32-33 grams applied to the scale, the replica was only 28 grams in weight. Fortunately, the dealer has the battery exchanged without objection against another - this fits well the weight and also the color of the print, but also came only in bags. Thus, there remains a residue of doubt as to whether the battery is really original; My expenses for the inspection, the correspondence with the dealers and the search on the Internet is in any case out of proportion to the (opposite the Amazon price) saved money. Another battery, I had directly ordered at Amazon, that came to a complete Samsung blister. So if you want to make sure that the battery is really original and not just a well-crafted fake should buy (in my opinion) rather at Amazon itself and not in a marketplace provider.
At runtime, the battery I can not say anything, I used the battery is currently only as a reserve.
Ultimately, I think it is a job for Samsung, which make batteries tamper-proof; Nokia has introduced eg a hologram on the battery for years ago. In Samsung there is nothing like that. While I am quite satisfied with the capacity of the battery, falsifying safety would be (especially in view of the dangers of substandard lithium batteries) urgently. Therefore, there are only three stars from me.
