When you upgrade from the old cell sites to the DECT cell sites, you need to follow a certain procedure. Panasonic's partner website has the migration tech note somewhere. If you haven't done this, that is probably why the new cordless phones are acting weird. The first time I swapped 0141 cell sites for the 0155s, I didn't follow the procedure and had problems. I had to go back and re-initialize the system and follow the migration tech note.
The CS not connected message usually means that the cordless phone is out of range.
Your power issues might just be a bad power supply, you are not exceeding the power consumption.
