From experience, I would buy an original Sony battery - through ebay or amazon. By time, I'm learning that in photography (as in other things) the cheaper ends up to be more expensive; as it would need to be replaced sooner.
Lately, I bought 2 generic batteries for my sony a580. I admit that they were cheaper, but one of them seems to loose the charge faster and does not display the remaining percent. The other works all right.
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Sony α580 dSLR
Tamron 17-50 2.8, Sony 18-55 kit lens, Minolta AF 50mm 1.7, Minolta 28-105mm xi zoom, Minolta 35-70mm 3.5-4.5, Minolta 75-300mm 4.5-5.6
Kata 3n1-22
My short photostream:
ivandegi