As in all GE 90-30 IC693 PLCs, the backup battery for the IC693CPU374 is located in the power supply that is plugged in to the same base plate as the CPU374. To access the battery (IC693ACC301), go to the door at the bottom of the power supply and gently pop it open, lift open the door, make sure the wires come out cleanly, and then gently remove the plug from inside.
Take the replacement battery and plug it in into the same socket. Make sure that the battery light goes out. Put the new battery into the door and carefully put the wires back into the power supply, and close the door.
This process applies also to the GE IC693CPU372. We recommend that you replace batteries with the power still up on the system; this way you can be assured that the program and the configuration will be retained during this process.