People will sometimes shorten this to say that the swap "supplies battery," particularly in conditions like test tools or army subject phones the place it isn't always apparent which end battery energy will come from. Within the case of change-supplied energy, AC-DC rectification was an imperfect art and there was a necessity for a backup capability in any case, and so the phone change would get its loop low voltage armored power cable from a very massive battery. I'll principally ignore this, but know that among the parts of the phone change may actually be in a curb cabinet in your case. These curb cabinets often operate as remote components of the swap and join back by ISDN or fiber.