One of the most critical and potentially catastrophic failures you can have in any GE 90-70 PLC-based control system is to lose the program in the PLC's CPU.  Fortunately, all PLC CPUs from manufacturers like GE provide a battery to back up the memory in the CPU.  But, the battery will run out of juice at some point and you will need to replace it. Here is a video that explains how to replace the battery in a GE 90-70 IC697CPX772 CPU: How to Change a Battery in the GE IC697CPX772 .  One great feature of the 90-70 CPUs from GE like the IC697CPX772 is that you can change the battery while the CPU is powered ON so that you will not lose your program or any of your register memory. After watching this video, if you still have questions or issues with your IC697CPX772, please contact our GE 90-70 PLC hotline at 1-800784-9385.