BT DECT handsets and base units (Sunnyside RH19)

Four fully working DECT handsets, plus one handset that works but the display is blank. Four charger bases and one digital answerphone base - all with mains power supplies. The answerphone is untested (I've never used one) but I've no reason to think that it's not working OK. These are quite high-spec handsets that synchronise with one another (so for example if you set the day/time on one handset, all the others get updated).