I didn't know they include a spare standard battery in the box, so I bought a separate one and had to return it. This charger and extra battery has saved my ass more than a few times.
I have this dock, and a extended battery, it's actually very useful, I bought mine off Amazon. As I'm using my extended, I can have my other charging to just carry or what not. And it comes with a extra battery, so don't worry about running out of battery life, lol.