Robsyuk 2018 Levorg Sti

Landed back from Florida this morning and while struggling not to fall asleep I decided to replaced my faulty 2nd O2 sensor.
Fault code cleared, and genuine sensor installed.

Wheel off, access cover removed, heat sheild off and half hour later it's done
Now at 98838km (61400 milses)
Cvt oil pump seal and oil change next.

2 weeks in America, I come back and the car fires up instantly. Drive it a little and a few days later it's dead.
I assume I left something on, but after 2 days on the battery conditioner / charger, the battery was only showing 3v!

Quick trip to Halfords, grab my favourite battery and she's alive! Now at 988890km