Hi shaun
Had probs with my batt a few weeks ago, old batt no good got new batt wouldnt start ,AA checked new batt that was sh*ged rest of the car was fine 2nd new batt now fine.
Any way when switching off ignition their is an electrical buzzing from engine bay untill i switch off batt master switch.
Dont know if this helps but that buzzing has got to be a drain???
Any way good luck cat boy
Ex acadamy car 2002, yellow and black 😬