I have an update:
I have been in contact with the folks at the Odyssey battery headquarters. They are very helpful folks. They have instructed batterymart.com to give me credit under warranty for the 6 month old battery.
They tell me that the primary reason for an Odyssey battery to have the symptoms that my 6 month old and 3 year old battery had was sulfation.
They also gave me a special procedure to follow to desulfate the battery if it can be saved. The prodedure is to discharge the battery at the 5hr rate maximum down to ~10v OCV. For the PC680, that is 3 amps max. And then to use the 6 amp Ultimizer to recharge the battery till it goes into trickle mode and to do this as many times as needed as long as the discharge time keeps taking longer than the last cycle.
I found my oldest battery (never threw it out) with a date code of July 09. It was replaced back in the fall of last year due to the same symptoms. I wanted to see if the special procedure could bring this thing back to life. So far I have completed 3 cycles on the battery. The first lasted about 5 minutes, the second almost 2 hours, and the third was well over 4 hours and tonight I plan to try another one. The bottom line is that this procedure seems to be working to revive this battery.
The only thing the support from Odyssey cannot explain is why these batteries are getting sulfated so quickly or at all in this application and with the continuous use of the Ultimizer charger.
I am a bunch more educated about these batteries now and I think the new one is going to last a long time even if I have to perform regular desulfating procedures on it. I still do not plan to keep it on the Ultimizer continuously.