Need a new battery!

My Z1000's battery has sh1t itself and will no longer hold charge.
Clearly I need a new one, but where the hell do I get one from?
Is it best to go to a bike shop, Repco or go to the manufacturer?
What sort of cash am I looking at?
Has anyone with a Power Commander noticed that it drains the battery, when left stationary?
This is the battery I need:
Daz.
Clearly I need a new one, but where the hell do I get one from?
Is it best to go to a bike shop, Repco or go to the manufacturer?
What sort of cash am I looking at?
Has anyone with a Power Commander noticed that it drains the battery, when left stationary?

This is the battery I need:

Daz.
