The amp hour figure is a measure of battery capacity. It is directly related to the size and weight of the lead acid battery.
CCA is a measure of how quickly the battery can release its stored energy, to provide current to a high amp load, like a car starter motor.
While battery capacity is directly correlated to battery size and weight, CCA numbers can vary widely among batteries of the same weight, depending on if they were designed with many thin porous lead plates for maximum surface area (starting batteries) or constructed with thicker denser plates designed for slower discharge cycles, and many more of them.
Many AGMs will have high CCA ratings due to less internal resistance and are better dual purpose batteries, than flooded batteries designed as dual purpose batteries, like Marine batteries which fall inbetween true deep cycle and starting. Marine batteries will put a deep cycle sticker on them, but a true deep cycle battery is constructed differently.
With most AGMs the difference between a starting battery version and the marine version is the addition of threaded studs in addition to automotive posts, and warranty, where as flooded batteries are internally different.
So there is no way to get 100 amp hours from a small battery. Ignore the CCA specs when looking for a battery which is to be cycled. The CCA figure is not important unless the battery is going to be used to start the engine.
Reserve minutes are another measure of capacity and this is kind of a confusing measure of capacity. The standard measure of capacity is the 20 hour rate, and I feel other rates like the 5 or 10 hour rate or reserve minutes are deliberately misleading when applied to a battery.
If your solar controller says to get a hundred amp hour battery, then a group 27/ 29 or 31 battery is what you need to look for, and anything else, any other size battery is not going to fall in this hundred amp hour range. There is no way to stuff more capacity into a lead acid battery. It is directly related to size and weight. 100 amp hours capacity is going to be right around 60 LBs. There is no way around this with a lead acid battery. Beware of the marketing departments. They are clueless about their product, except on how to maximize sales, and this is basically trickery with the OK given by what the lawyers find to be acceptable risk.
And yes a 100 amp hour battery only had 50 amp hours available to use, but no need to try and outguess the intent of the recommendation.
OOne more point I should clarify is that AGM batteries weigh more than flooded batteries of the same rated capacity.
I have a group 27 Northstar AGm rated at 91 amp hours which weighs 74 Lbs,
and a group 31 flooded battery rated at 130 amp hours, which weighs 67 Lbs
So compare AGM to AGm and flooded to flooded.
BTW my AGM blows away the Flooded battery in terms of voltage held under load, and CCA. The fully charged AGM can start my engine so quickly it is scary, where as the fully charged flooded 31 is a wimp in comparison.
