i found battery life bad out of the box. i updated and it was better. then i installed the beta OS 2 and it was good but not great. i then did a security wipe, reverted to OS1, latest, and it was great. updated again today and all seems great still. getting better all the time.
I have the exact same problem as OP. The battery life is horrible!! Wifi on, BT/Bridge off. Screen brightness turn down to 40%. Latest official update.
I did a security wipe and updated the OS. I think it's because standby mode doesn't actually power down the wifi idle mode. I'm leaving my wifi off and will report back!
This morning the battery gauge was indicating 0 % but I was still able to use the PB. I will check tonight if it is still working and how long I can work at 0 %. Maybe it is just the gauge that is not accurate.