My phone says to register HS see manual but can't find out how to regi

I just purchased a VTech DS667V-2G with four additional handsets. Only the base station handset registered, all the others continually failed. I finally fixed this by placing each handset on the base station in turn, once on the base station they automatically registered. I then put them in their chargers around the house and they continue to work. It is unclear why this works but not on their own charging stands, but anyone experiencing this issue should try this before calling for tech support, the response on VTech's site is not helpful.