Intermittent Electronics Issue - Ford Focus Titanium 12plate

I have a strange recurring issue that I'm hoping everyone can suggest some things to check. The focus (Titanium 12 plate) starts fine on a daily basis, running around town, etc. Twice I've now had it that I leave my car at work and take a work vehicle for a period of around 10 days. I take the key with me so I know it's not moved or opened by anyone at work. When I come back to swap to my car the car will start fine and do the trip home (about 15 miles / 30 minutes). After 24hours parked at home the battery is totally dead, it won't even unlock the central locking. AA have jumped started it on both occasions and done a battery test, battery appears fine and is getting charge from the alternator. No warning lights on the dashboard, nothing left on over night such as lights etc inside, nothing plugged into the USB or 12v sockets, all lights are working so no blown bulbs on head lights / indicators / etc, all speakers are working so no apparent break in those cables. I'm looking at an expensive bill for diagnostics so hoping to reduce the number of options and investigate further before I send it in. Thanks in advance. My next plan is to see how long it takes to drain by checking it every few hours to see if it will unlock so I have a period of time that it takes to go flat.