I have one original canon bp 500 battery and one hahnel equivalent for my 10D.
The difference in performance is negligible,and personally I don't think it's worth the extra price.

Just my cents from my experience in the HAM handheld radio world. Similar to the camera world, manufacturer-branded batteries cost a lot more than 3rd party batteries. There are extremely reputable 3rd party battery manufacturers and that's all they do. They make products that are plug compatible with name brand, last longer, cost less.

Unofrtunately there are fly-by-night 3rd party makers that produce junk. It will take some research but the reputable ones will start to stick out like a sore thumb once you start digging on the various sites.

It's entirely possible that Canon doesn't actually make their own batteries anyway and that they are sourced from any number of other manufacturers. I wish I knew a site that documented this.

Are the non-OEM replacement Li-lon batteries for Panasonic Fz5, or any camera for that matter, acceptable?
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My $25 walmart replacement battery failed because its contacts corroded.

My $11 sterlingteks seem fine.  I haven't had them as long as the walmart battery, tho.

Edit: All of those batteries were for Canon.

thanks for all your comments.  am going to get the non-oem.