If the CS55 is working sometimes, but having a hard time charging, try cleaning the charging contacts.
(usually you’ll have to push extra hard when placing the headset in the base to get the amber light to flash)
Make sure the lights are on in the base, if they are on and working correctly, clean the charging base contacts with an eraser, and the headset charging insert with a toothpick (these are the copper prongs that stick up from the charging base, as well as the charging insert on the headset). Most times, that will work. Recommend that they try cleaning those contacts every so often. If this does not work, try the usual troubleshoots up to and including a battery reset.