Battery Replacement 1 1 The PARTNER ACS processor module uses two user-replaceable AAA alkaline batteries. These batteries provide enough power to retain the system programming settings during a power failure for 45 days to six months, depending on the freshness of the batteries. When battery power is getting low, the system displays a ChgBat W/PowerOn or ReplaceSysBat W/Power On message on the top line of display telephones at extensions 10 and 11 in place of the default day/ date/time message. Users at these extensions should be instructed to notify you when they see this message. You should replace the batteries within 45 days of seeing the message.