Mine didn't work either. I notice that the contacts are recessed about 1/16" from the end of the battery. All the other batteries I've seen, the contacts go almost to the battery's end.

But I tried charging it in an external charger too - one with long contacts (and a built-in light show), and it wouldn't take a charge. And it fits snugly in the N810. So I don't think the shim would have helped me.

Customer service responded quickly, is sending a replacement and crediting me for return postage. I will report back on the replacement.

In the meantime, I am doing battery capacity tests on my batteries. I use battery-status to record the voltage levels to a file. Rather than type the whole command line every time, I've created an icon in Personal Launcher that runs the command. So I don't have to wait a week for the battery to run down, I turn on bluetooth, then run Flip Clock and turn on Insomniac Mode. For good measure, the browser is running in background, pointed to a web page that refreshes every five seconds. With all this going on, my spare battery ran down to the low battery warning in under 6 hours.