DS3 Terminal 30 Battery Drain

Sounds frustrating. 'Terminal 30' usually refers to the constant positive feed, so something is keeping a circuit alive when it shouldn't be. Before diving too deep, have you tried checking for voltage drop across the main fuses? Any recent work done on the car that might have disturbed the wiring? Could even be a dodgy ignition switch or starter motor solenoid. What's the battery voltage reading when the car is off?

Voltage drop across the fuses? How exactly do I check that? No recent work, although she did have a new radio fitted a couple of years back but it's been fine since then. As for voltage when off, I'll need to get the multimeter out, won't I? Where should I test from?

Okay, cool, so the radio install might be a red herring. For voltage drop, you ideally need a multimeter that can read millivolts. Put the meter probes across each fuse (without removing it). A healthy fuse should have a reading close to zero. Higher readings indicate a voltage drop, meaning current is flowing through that circuit when it shouldn't be. But honestly, with it being 'Terminal 30' and given the starting issues, I'd strongly suggest getting it checked by a workshop. Could be a pain to trace that fault.

Appreciate the input. Workshop it is then! Turns out the battery was duff and they found a parasitic draw on the starter motor circuit. New battery and a bit of wiring sorted it. Cost me 290€ all in. Thanks again for your help!