I had the same problems as noted by others in the forum and they were successfully resolved today.
Problems - Upgraded to 1.3.1
- Battery life went to 0% in less than 6 hours when phone was not in use at all - no talk, no surfing
- Annoying (repeated) notification that Y! was requesting me to reenter my password
Solution
I did the following things -- sorry, not a controlled experiment with changes to only a single variable:
- Reset network preference to Sprint only - no roaming. As noted in earlier posts, the 1.3.1 upgrade reset my network preference.
- Removed Y! as an email, contact, and calendar account; left Y! as a Messaging account (I use Y! Messenger)
- Ensured that I was signed off in Messaging
- Rebooted
Today, battery life is 50% after 18 hours of mostly standby use. Problem solved.