https://wowelectricals.com/product/siemens-6es7971-0ba00-back-up-battery-3-6v-2-3ah-f-ps405-407/
Siemens 6ES7971-0BA00 BACK-UP BATTERY 3.6V/2.3AH F. PS405/407 - WOW Electricals
Aug 3, 2020 - SIMATIC S7-400, Backup battery 3.6 V/2.3 AH for PS 405 4 A/10 A/20 A and PS 407 4 A/10 A/20