The Siemens SIMATIC S7-400 Backup battery 3.6 V/2.3 AH, 6ES7971-0BA00 for PS 405 4 A/10 A/20 A and PS 407 4 A/10 A/20 A. The Siemens SIMATIC S7-400 Backup Battery 6ES7971-0BA00 is a lithium thionyl chloride battery designed to provide backup power for the SIMATIC S7-400 PLC system.
Lithium thionyl chloride batteries are known for their high energy density and long shelf life, making them suitable for backup applications.