Using your Xperia Mini Pro off your first full battery charge might shock and disappoint you – the battery will discharge fast and in about 4-6 hours reach 10% - 0%. I read about this before my purchase, but now also know this to be true from experience. It does not make a difference if you charge the battery using USB off a computer / laptop or the AC mains plug.
THE GOOD NEWS: Your battery absolutely will improve after a few more recharge cycles. My battery now lasts over 48 hours off a single charge. This is achievable for both Xperia Mini and Mini Pro. Most smartphones last 24 hours on a single charge with usage (e.g. iPhone 3GS, HTC Desire…) so to be able to get 48hrs is absolutely brilliant.
I will write up a post detailing steps on maximising and optimising battery life to get the full 48+ hour results.
FURTHER GOOD NEWS: When Sony Ericsson finally release Android 2.1 or 2.2 (or when we can ROOT the phone and install it ourselves) it will automatically improve battery performance simply through the improvements made to the Android OS.