3 cordless Telstra phones V580 5.8 digital & answering machine?

I have the user guide but it of no help. 6mths ago the no 2 phone stopped working and charging( changing the batteries over did not help. Recently no 3 in set has done same. These phones were puchased with fly by points from Amx approx 2years ago. We need 5.8 because husband hard of hearing.these phones were great 2 teenage girls move them all over the house and forget to put htem back on charge but we are retraining them. The main still working and answering machine but not sure what to do next.? Main is in bedroom with answer machine 2 is in room next to bedroom. 3 is in the kitchen the next room along.