Cheap vs. OEM batteries?

[BSquared]

So... after the first couple of posts I ordered an expensive "real" Panasonic battery from Amazon for around $15. However, I blew it and bought the wrong size, so I returned it. Then I bought a $7 one. Haven't had a chance to do anything extensive, but it charged properly and it definitely works in the camera. I'll update after taking it skiing, a demanding test because of the cold.