Kindle PW2 battery issues 5.7.2.1

Hello,

I recently upgraded my PW2 (not jailbroken) to the latest firmware 5.7.2.1. Now my battery life has suddenly become quite poor! Has anyone else experienced this?

Being relatively new to kindle/firmware, I looked into downgrading to an earlier version of the firmware but the device doesn't allow that....

Any suggestions or thoughts will be appreciated!

Thanks