Calibration was done 3x afterwards. All were in the same range as the original slope. Chainring bolts were torqued to suggested 10nm. Now I did crank the crank bolt pretty tight since its an FSA and my torque wrench doesn't go that high. I wonder if that may be the reason for the higher then normal zero offset (when in the house at a steady temp it's in the 800 range up from the low 600 range before the battery change). As I mentioned the zero offset is stable. Just high. When I went to check the zero offset after doing a couple hill repeats it was around 1400 so I'm not sure if this is due to some sort of residual strain in the gauges. But the power numbers were accurate based on previous outputs.
Where I was having the big issue was with temperature. It seemed when the temp was hovering around 0 (32 for you guys to the south
i was getting all sorts of wonky numbers. 55 for a zero offset and 65watts going uphill.
Since the numbers, now that its above freezing, seem to be ok now this may all be a moot issue. Still I'm curious to know the reason behind all this in case it becomes an issue again in the future.