Hi ! When I used BG44K, I did one full can it into a full tank of fuel and ran it down to empty before refilling. the reason was a) not to dilute the solution b) this stuff needs time to break down contaminates in the engine and fuel system and running a full tank down gives greater opportunity.
Also I know this stuff works and found it worthwhile to do it after the next 10k.
In the UK we do not have the range available that you have in Canada and the States so this is probably the best we have!!!
There are companies in the UK now offering the full fuel delivery clean where they link your car to a separate fuel supply with all of the cleaners for about £85.......
What is an issue for all cars but especially the 6 series as you are now aware is the battery, and really cold conditions (but nothing compared to other countries) can have an affect!!!!
Always said I would go back to a 6 series