The Guardian charging extension can either be used independently to charge 3 handsets (PSU & 3-pin charger cable required). These can be daisy chained together (up to 5 sets off one PSU) to charge up to 15 handsets in total.

Alternatively the 3-way extension can be added to a 4-way charger/configurator (up to 4 sets can be added to a 4-way charger) to charge up to 16 handsets in total.