actually, i was talking about the grip for portrait shots, not about battery lifespan. my battery lasts me pretty well on shooting trips.
How would you expect a battery grip to perform?
Just attaches on, holds two batteries, gives a vertical release, AE lock and AF point select buttons, and an added dial for exposure setting adjustment. It also provides added shooting comfort when shooting in portrait orientation.
Think that's all though...
Obviously it'll add some bulk so if compactness is an issue, then this may be a no-go.