Battery == consumable item
Then... buy a new battery, or ask your carrier for a replacement if you have a service plan?
Try one of the beefed-up Seidio replacements available at Amazon for around 40-50 quid. The 2700mAh in my 9700 goes a week between charges.
Incidentally, along with the unified messaging screen, which no other mobile UI seems to get right, monster battery life is the principal reason I've stuck with BlackBerry. If other manufs. can improve on the de facto standard crappy 12 hour life of smartphones generally I'd be quick to switch.