Make sure you only add distilled water not tap water. Actually running a CCA test might damage a deep cycle battery. Find a dummy load and run a test like I outlined above. It at least gives you a relative indicator of the capacity left in the battery. Here are some curves on batteries discharge. Try not to geek out. If you can find a large high power resistor you can use that but it will get hot.
You need one of these. You can adjust the resistance from 25 ohms on down to get the load you want. You can measure current using ohms law and measuring the voltage drop across the resistor. I=V/R and also measure the voltage across the battery. P=IV to get the watts dissipated in the resistor. You need to keep track of the hours it takes to get the voltage down below 11V or whatever the manufacture considers dead.
There are some USB data loggers on Ebay cheap but they have a 5V max input voltage. You could make a simple voltage divider circuit to drop the voltage to where the data logger can handle it. It all depends on how much time you want to spend to get your answer.
I would setup a Labview program to do this, if I were at work.