Their description:
Product Description
Compact and lightweight, this 1500 mAh Li-Polymer battery provides long-lasting power for your mobile phone…. More >>
Go & get it here - i can recommend it:
Nokia BP-4L Standard Battery for Nokia E61i, E63, E71, E90, N810 WiMax

Works great in my Nokia N810. The previous battery went flat after a period of inactivity, and the device would not start up or try to charge the battery. Putting this one in fixed all of that.
My N810 uses this battery. I ordered one of those imitations on Amazon, which turned out to be a mistake, because it died in 2 days. This one has worked for a month or so now.