Below are freely available pdf files of recommended texts for bat workers; professional ecological consultants, academic researchers, roost visitors or bat group members.
Bat Worker Guidance.
Bat Workers Manual – 3rd Edition (link to complete copy)
Bats and Onshore Wind Turbines (Interim Guidance) – Natural England TIN051
The excellent Eurobats series of publications
Illustrated Key to the Bats of Europe, Dietz & von Helversen. Part One
Illustrated Key to the Bats of Europe, Dietz & von Helversen. Part Two
Many of the techniques and survey methods in the above documents require a person to be a licenced bat worker.