Logix 5561 PLC was shut down for a day. Started found battery red light, green light in ok and run, I/o, rs232 in off
communication error in HMI. What is the issue?
I recommend you to google the manual of this CPU. There is very likely a section where the indication is explained.
The battery in the processor was dead. When you lost power, the program was erased, since the battery wasn't available to keep power on the memory. The HMI is showing errors because there are no tags to read in the PLC. You'll need to download the program again.
For what it's worth, the more modern 5570 and 5580 processors do not use a battery. They have a capacitor, and when power is lost there's enough power to move the program and data to flash.
Sage Automation, Inc.