The aurora moves faster than the photographs suggest. Anything over four seconds and the structure smears into an even green wash — pretty, but it stops being a picture of anything.
Fast glass matters more than a good sensor here. f/1.8 at four seconds beats f/2.8 at eight every time, because the second exposure is photographing a different aurora than the one you framed.
It was cold enough that the second battery went in after eleven minutes.