What it is and where it fits
The Siemens 6ES7971-0BA02 is the factory-specified backup battery for SIMATIC S7-400 power supplies — specifically the PS 405 and PS 407 units rated at 4 A, 10 A, and 20 A, including extended-temperature variants. It delivers 3.6 V at 2.3 Ah, which is the capacity needed to maintain the S7-400 RAM and real-time clock during a power loss or when the rack is unpowered for service.
Regulatory compliance
RoHS compliant since December 1, 2014, and REACH Article 33 candidate-list information is available for downstream supply-chain reporting. Export control classification is AL: N / ECCN: N, so no special licensing is required for cross-border shipment.
Physical fit and handling
Packaged individually, one piece per unit, with dimensions 17.6 x 12.1 x 1.5 cm — sized to fit the battery compartment of the S7-400 power supply module. The 2.3 Ah capacity is the extended-temperature rating, so it holds charge longer in warm cabinet environments than the standard 1.3 Ah option.