[Al Skierkiewicz]

Ken,
Again there are too many variables for that. The age of the battery (how many charge discharge cycles) affects the surface composition of the plates. A battery capacity has a lot to do with how much of the plate area is actually exposed to the electrolyte. As the lead oxide builds up, less surface is in contact with the chemical. There are some testers available from automotive suppliers that put an instantaneous load on the battery and measure the current. Unfortunately, many of these devices are attempting to discharge over 100 amps and the meter isn't calibrated for a lower amp hour battery such as ours.
Ben, the CBA at 7.5 amps will take a few hours to discharge the battery to the specified terminal voltage of 8 volts. We will typically put a battery on test when we start the class time and watch it periodically throughout the night. Recent batteries have shown a failure in one or more cells over the discharge. Graphically, the battery will run at normal discharge until one of the cells stops producing current, at that point the output voltage falls by 2 volts. We have had at least one battery that had two cells with reduced capacity. Without doing a CSI on the battery, I suspect defective attachments to the individual plates in those cells. Reduced plate surface area=reduced capacity=reduced charge current/chemical action.
I don't have a graph here at work, but I do believe I have some at home. I will try to post this afternoon.