The first bad one was the battery I bought for my 7D, which I also mention in this post. That battery lasted about 1/4 of what the OEM battery would. I got a replacement from the seller, but by the time I received it, I already sold my 7D, so I didn't get a chance to test it.
The Sony NEX-5 is a battery hog and it doesn't last very long. It's a far cry from more than a 1000 pictures I could get out of from a Canon camera. In fact, the third party batteries in my 1D IIn lasts at least two thousand pictures. I hardly need to charge them. So, I bought a NEX-5 compatible battery from eBay, and it arrived in two days, since it was shipped from the same town I live. Immediately, I had a bad feeling about this battery, as it weigh quite a bit less than the OEM version. This battery, like the 7D version, never charges to 100%. Regardless how long you charge it, it always says 99%. It lasts about 1/3 of what a Sony OEM battery would. E-mail the seller, and got a rude responds, to the affect that I should not expect OEM performance because I didn't pay OEM price.
My worry is that these are not isolated incidents, but a trend that quality of third party batteries are going down the drain. Perhaps the seller was right, I didn't pay OEM prices, I should expect OEM performance. Perhaps I should stick to brand name third party batteries, like Lenmar and Optex.
Canadian Ranger Toronto -- NEX-5 & Carl Zeiss S-Planar 60mm f2.8. Click to see larger.