Possible Alternator Problem?

[WakingJudea]

A while back I had a 220 amp alternator installed from http://www.dbelectrical.com/ (I know its nothing special) and I haven't had any problems with my charging system until I started running my amp at a 1 ohm load from a 2 ohm load. I have a T1500-1bd RF pushing two AA Chaos' 15's and before that i had the same amp pushing 2 CVR 12's at 2 ohms. I recently bought a used Odyssey PC1700 battery from a friend and hooked it up, been working fine for about 2 weeks then all of a sudden the check charging system light came on in my 05 Ford Taurus after ive been bumping for maybe 10-15mins driving around not sitting idle. So I decided to see how much voltage my amp was seeing and hooked up a stinger volt meter directly to my amp and it was seeing no more then 13.9 idle, even when I revved the engine. Next I decided to see if it was the battery that was no good by hooking up my previous battery, a Diehard Platinum P4 which is just about the same IIRC and when I hooked it up my amp was seeing a steady 14.0 volts at idle and 14.2 when i revved the engine. I went for a drive and started bumpin like normal and on my way back home after I had turned it down the check charging system light came on and my volt meter was reading 12.2 - 12.4 volts even if I revved the engine. I have a video of my big 3 to help see whats going on under the hood http://www.youtube.com/watch?v=eIuubkC6GjU I forgot to mention the battery up front is the only one installed at the moment, I do plan on putting two 93ah C&D Technology battery's in the back and upgrading the RF to a Crescendo 3k. Does anyone know whats going on or what I need to check out next?