I have been cosidering replacement batteries for a little while. My 99 6.5 K3500 takes group 78 batteries. I had decided on a pair of 850 CCA dual post batteries when another member posted "food for thought".

"....... the highest CCA you can get for a certain case limits electrolyte volume because lead takes up the space and thinner plates fatigue sooner killing the battery- 1 size smaller will give near equal power and last longer in most cases of liquid filled battery's."

So I went and found the specifications for a group 78 battery (see attached). It turns out group 78 batteries are rated for between 465 and 800 CCA. That makes me think to get 850 CCA the plates were thinned and the battery is more susceptible to vibrations and sulfidation.

I think ill take racers advice and get some 700 CCA. It should be ok considering I am in the low lands of western Washington where temperatures rarely drop below freezing.

If anyone has a modification that fits a larger battery in please let me know.