AGM batteries longivity ?

I'm plugged in twenty four seven and I exercise my batteries as well. I unplug for a week or two then plug back in and check my battery levels once a month along with running the genny for a 1/2 with a load on it and with this Orange County HEAT in California I've been visiting my Toy Hauler to escape the heat and enjoy the air conditioning Note: My rig is in my front yard. I ran AGM along with my regular battery had no charging issues now I run two 6 volts and I've never have looked back. I have the stock charging system that came with my trailer nothing special. I do keep an eye on the meter with one of these Digital Battery Monitor with 12-Volt Adapter:

http://www.walmart.com/ip/Everstart-932W-Everstart-Battery-Monitor/16139506