When I got my SX30-IS last year, I got an extra battery
just in case, but so far haven't depleted the first
to the point of having to change while out and about.
I always top both of them off and rotate before leaving.

When shooting in /very/ cold weather you may find it helpful to keep a
second battery in your (warm) pocket for when the first starts to show
lack of power. When shooting several hundred pictures per day I have had
to change batteries very occasionally with my Nikon DSLR. I also follow
your top-up, rotate and change on a nightly basis when a shoot is
critical, but perhaps not as rigorously as I used to.

Cheers,
David