I wasted a lot of money on an alternator controller that produced pretty much zero benefit, given that my alternator is already charging at 14.4 volts. I second Roger's recommendation to read Gibbo's musings before you make any decisions...
As an aside, the controller was a Sterling and I found their customer service approach not to my personal taste depending on who answered - on a lucky day, one particularly kind and helpful individual who was a pleasure to deal with, and on another day a somewhat tiresome individual who was possessed with absolutely no 'soft skills' whatsoever...
After the unit failed for the second time I gave up trying and went back to the original installation, poorer but wiser...