I've always believed the opposite what is stated above, that the higher the CCA of a battery, the better it is and will last longer. It is a misleading statement when all things are considered. In terms of robustness, a lower CCA battery will be more robust than a high CCA battery given same case size.
First, the higher the CCA of a battery (and let's assume the plastic-cases are all the same dimensional size for comparison), a 400CCA battery as compared to a 250CCA battery will have to have more lead plate surface area, thus thinner lead plate thickness to fit into the same case in order to achieve the extra CCA capacity. Thus, a 250CCA battery will have thicker plates in the same sized case as a 400CCA battery. The 400CCA battery will give more CCA, but at a cost of thinner plates and less space between plates for electrolyte.
What does this mean? Thicker plates are better for high vibration situations. Thicker plates with more space between plates will result in less sulfation crystals forming and touching adjacent plates shorting out individual cells.
A well constructed 250CCA battery will actually be a better constructed battery as compared to a 400CCA in the same sized case.
So, my recommendation (not that it was asked) is to use the CCA battery rated for your purpose, and buy the best quality battery at that rating. If your tractor calls for a 250CCA battery and you put in a 500CCA battery that has the same dimensions, you will be getting a much less robust battery in the 500. Yes it will give more power, but robustness is compromised.
Like many things, the Devil is in the details.
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