Battery grip question

I have a question about the battery grip for the K10D.

After having some issues with the focusing speed of the DA*300, several posters have suggested that battery strength is a factor.

I would therefore be interested to know how the extra battery in the grip operates. Is it selectable, or does the camera just use both simultaneously.

Basically, would the addition of an extra battery in the grip improve focusing speed, etc.

Thanks

Two Jugs

--