I did the last update on mine with only ignition on and it works.
But I would really recommend to connect a intelligent charger with around 10A or higher as all electronics in the car use a bit when ignition is on.
Used a Ctek MXS 25 when I updated.
RS Edition , built 13/9-18 , and delivered 9/11-18
Mountune: R.M.M. / Roll restrictor, PTU Brace, Breather plate & Re-circulating valve.
Mishimoto: I/C + pipe kit, Catch can, Blue Aluminum expansion tank
Ford Performance / Remus cat back Exhaust
FSWERKS short shift kit.
quantiTEC Smoked rear lights.