I bought this battery on eBay for $24.98 (including shipping), based on your comments, and it seems to give me a few extra hours of power. As recommended by the manufacturer, I fully charged it before installing it, and ran it all the way down before fully charging it again and repeated the process once more. It got better each time. So far, I'm happy with it. But if my usage increases dramatically, I'll buy the Seidio 3500 mah. But that means I'll have to give up using my current Surface case. Ah...compromise, compromise.