Something like:
Battery (3.7V 1530mAh 5.66Wh)
http://www.amazon.com/MiFi-Battery-3.../dp/B003MQAT82
Amazon Kindle 1 Battery (3.7V, 1530mAh)
http://www.amazon.com/Amazon-Kindle-.../dp/B0047CAJYO
Make sure that battery plug fits PocketBook Pro power connector
Charger - make sure that it is 1 AMPER
Firmware - no reason to upgrade