At what brand name batteries cost, I go for the aftermarket ones. They don't seem to last quite as long or maintain performance quite as well over time, but for the price, and this making it easier to always have backups charged and ready to go, this is one area where I create electronic waste for the county to take care of, rather than spending big. I have used 6 aftermarket batteries and the one original factory battery during the almost 8 years that I have shot my 10D. The last two aftermarket batteries are a recent purchase. That's about one battery a year, on average, but I use a double battery grip a lot of the time, so I consider it more like a 2 years per pair average. I was set back $32 for the most recent pair at Freestyle. I got the four previous aftermarket ones in a bunch for $27 shipped on E-Bay.