Messing around with features such as the camera, music and internet are probably the most likely causes. My K800i dosn't last for long when these features are greatly relied on. A few things you can try:
* Lowering the brighness
* Using flight mode when relying on the Walkman and Camera for long periods
* Keeping the volume lowish on the Walkman (If you can bear it
)
* Keep the phone on charge where and whenever possible
* Turn down the ringtone volume if recieving calls frequently
If the battery life does appear to indeed be a fault with the firmware, just keep it cool and wait until SE come out with a patch up for it. If the low battery appears to be a hardware issue with a few batches of the models, then I would suggest returning it under warrenty if you have a faulty W580i
.