Yeah, that's my understanding too. I think the load tends to be much higher with high-output alts but for shorter periods. Makes me wonder about efficiency. From the little I know about it, electrical power draws in a car sacrifice ~10% power. I'm trying to cut that down without resorting to under-driven pulleys.
Personally I try to keep my battery charged to 100% all the time. I know it really helps battery life and I suspect it helps fuel mileage as well. A few more miles if the alt dies wouldn't hurt either.
I might wire a pigtail up permanently...my new
Xtreme Charge seems like a pretty nice little unit, works well so far even on AGM and VRLA batteries. The "de-sulfation" stuff seems a bit far-fetched but so far it's a nicely self-contained and durable unit.