Optima Red Top bad?

[Happyfunballs]

I have an issue with my charging system. My voltage fluctuates from 13.6 to 11.1 volts when certain accessories are switched on. I fluctuate .6v when my blinker is on. I consistently have 13.6v at the single wire alternator when the engine is at, say, 1200rpm.(I read somewhere that certain alternators will not charge at idle, I apparently have one) I'm suspect of the battery, as I haven't treated it nice over the years. It's roughly 6 years old with 900 miles on it. That doesn't count the number of times it's been pulled out of the garage, brought up to temp and put back in the garage. I've never trickle charged it over the winters so I imagine that's not good for it. Is it time for a new battery? Should my alternator be putting out 14V? It's a 100amp running normal driving functions and a dual fan cooling system without a stereo. Lil' help here fellas. Thanks.