I am wondering if there is a sufficient hardware difference between 2GB and 4GB PW2 models that could result in the "battery drain issue", which doesn't seem to affect all PW2's that are beyond 5.6.5?
Went visiting to the PW2 Amazon product page, and started reading more recent negative reviews that mentioned sudden poor battery life. Customers contacting Amazon Kindle support are not being helped in any constructive way, other than to be offered a very small discount on a new replacement unit.... I made a few comments, asked some to verify if they have a 2GB vs 4GB model, and left Amazon links for updating to 5.7.3 Many of these folks have given up on their "battery-dead" PW2's. Very sad.
https://www.amazon.com/review/RPITG4EP627WG
https://www.amazon.com/review/R1ZEX3NDSWHDG7
https://www.amazon.com/review/RGOAOCPSYMIOA
https://www.amazon.com/review/R1XRUVI9YXNQQS
If you guys get any other "battery drain on PW2" reports, try to make a note if it is 2GB vs 4GB.... it's worth a try!
Also, my PW2 2GB on 5.7.2.1 which is now registered and in sleep mode, has not seen any appreciable drop in the battery meter for the last 25 hours... I will let it go another day before turning on the wifi to see if the battery drops quickly and to test out the "magic folder" for blocking an OTA update
Hope this helps