How long will these devices be able to be used on battery and what kind of battery is used?

I had a Stowaway or something like that, it was foldable, and you could even put your device on it to have it static in a good view modus (not necessary with N810). It costed 25 USD on eBay. So I find a price of 3x as much... high.

Also, I guess the support on the NIT for this Nokia keyboard is 1) because its a Nokia product 2) guarantees perfect integration. This is important for some customers.