I have a 2023 Expedition Sport with 600 ace engine. When it gets down to zero or below- it struggled to start without a booster pack. i put a brand new battery in it and still having issues. Was -8 tonight and would not start- even though engine temp was 60 degrees. Any ideas on what could be issue- dealership did recently put a tender plug on it- but i cant imagine that is draining battery

I have two Skandics with 600 ACE engines and I never plug them in to warm up unless it's colder than -25. Both start fine above -25.
Be sure to check your cable connections, at the battery and starter. Also check the ground.
It should start very easy at -8 !!

Something is definitely wrong with that. I've got the 900 ACE which supposedly starts better in the cold than the 600, but I've ran the 600s while working for an outfitter who owns a couple and at 0 to -10 they started with no hesitations. The coldest I've looked at a thermometer when I've used mine was -29 and it didnt act like it wanted to, but it started. And those were stored outside on a trailer over night and hauled down the highway in the wind, engine temperature was definitely ambient, with a 60 degree engine it should start like it was summertime.

When mine did that, it wound up being the starter. Left me stranded, on crutches with a bad knee, forgot my phone at the house, after crutching 10 miles back towards the village, about 3 of miles in overflow, a young man saw me, gave me a ride the last 3 miles to the village. Multiple bad decisions compounded by a faulty starter.