Hello & Welcome to Just Answer,
Sorry to hear of any issue you are having with your phones.
To help you with this issue, may I ask:1) The Model Number that is printed on the back or bottom of the MAIN BASE UNIT of the phone system you are working with? I only ask because you supplied two model numbers, and perhaps got those from the title page of a manual of some kind.
2) How many TOTAL cordless handsets do you have with this system?3) What is the AGE of this system?4) WHEN did this issue first begin (or was noticed)?