A genuine battery was almost $80, so thought I'd grab a spare one off the net for about $15 to my door.
It's supposed to be decoded to work perfectly with my camera, but it just won't hold a charge. 1.5 weeks in the camera bag since I filled it, and it's dead flat without being used.
It did that to me once before, but it had been in my bag about a month at that time.
My genuine battery sitting in my camera, will show no visible loss on the battery indicator, after weeks, and that's while keeping the camera clock running etc, so has more right to go flat than an unused one in a bag.
The one time I did get to use it, it dropped from "Full" on the camera, to 75% on the camera very soon

Now what I'm wondering, is whether this is a single faulty cheap battery, and that others have been fine, or is this common with all cheap ebay batteries?

Any experiences with copycat batteries would be greatly appreciated.
I haven't put this in Canon, because I'm interested to know about all generic cheap batteries, to see if this is one dodgy battery, or common with cheap copies in any brand.