Right i am aware this thread is a little older but i'd like to share my battery experience because i feel it will help.
First off i don't think i had any battery faults, my battery died pretty damn quick one 1 day of barely using it with just normal settings wifi, bluetooth off, 3g data on, this got annoying fast
The standard battery is 1200mAh, you can pick up a 1500mAh battery off amazon or ebay rather cheaply (around 4 pounds with free delivery)
After getting this battery i did a full charge, then used it till it was almost dead then fully charged again... on the first day battery was the same as the original... barely made it through the day.
Then i turned off auto rotation... wow the battery life increased hugely, by the end of the day in same usage as above i was left with 41% battery.
So i've tested this and found that auto rotation being turned off with wifi and bluetooth saves alot of battery (3G data on)
While testing though i've come to realise the accelerometer doesn't fully turn off even when the option has been unchecked, you can verify this rotating the phone in gallery and the background moves around with the phone.
None the lesss with the option unchecked, battery life increases plus the extra 200mAh
Battery for sale links:
1500 mAh Battery for Samsung Galaxy Mini GT-S5570 | eBay UK
Modern-Tech Replacement 1500mAh Extended Battery for: Amazon.co.uk: Electronics