PLC Battery

Dear All, 

      I've been used to replace the battery of a PLC. the technicians were afraid to loose the program. I know the battery is important, but I need to know why it's important and what it is used for? and what the structure of PLC to show the battery?

If there's some files or manuals explaining this I'd be very thankful. 

Hello,

Perhaps the following FAQs might help:

1-When should you replace the back-up battery on your S7 300/400 controller?

2-Where can you find information about the S7-300/400 backup batteries?

Important:
1-Always change the backup battery in "Power ON" mode, otherwise you will lose data in the user memory and the internal CPU clock will stop.

2-Change the backup battery of the S7-300/400 controller once a year.

3-S7-300 : section 1.1.3 "Backup battery/accumulator" (Entry ID:8860591)

4-S7-400 : section 7.1 "Replacing the Backup Battery" (Entry ID:1117849)