I bought similar product from DX, sku.18883 and has been charging about 10 times now without problem. It can charge the phone from empty to 70%.
I also bought spare lithium battery type 18650 protected, 2400mAh and an external charger for it (sku.04151). So I can replace the stock charger's battery when its empty (the battery is exchangeable). Just beware, some protected 18650 battery doesn't fit on the power adapter.
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.NET & Android application programmer