Siemens S7-1200 System Manual page 28

Product overview
1.2 Expansion capability of the CPU
Table 1- 7 Other boards
Module
③
Battery board
28
Description
Plugs into expansion board interface on front of CPU. Provides long term
backup of realtime clock
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG