I have read several places that you should not disconnect the alternator from the battery (the thick cable) without also disconnecting the field circuit (thin wire to the regulator) because the alternator will continue producing charge and with no where for the charge to go, it will overheat and eventually self-destruct.
Charging System Checks (Alternator Testing) (in bright red)
http://www.arcomarine.com/xhtml/Page...orTechTips.pdf (very bottom of the page)
Self build adjustable alternator controler (about 9/10ths of the way down, begins "important")
I think "If you have an internal regulator then you may have to dissect it a bit and bring out a field lead to a switch." is what you have to do if you have a one wire alternator (internally regulated).
You need to put the lead on a switch, not a button.
I have done this, and mainly charged the battery at home, but you need to watch it very closely. I forgot 2 or 3 times to recharge after a few hours driving (including some night driving) and the thats all it took. Wouldn't hold a full charge anymore. Car batteries aren't really meant to be used for more than a few seconds at a time.
I just put in some RV batteries today. Hopefully I should be able to remove the alternator belt altogether, and avoid even the power loss from the freewheeling alt pulley.