[wagonman76]

I think a switched alternator and extra battery is a great idea. Just think last time your alternator died, you were probably able to go quite a ways with it not working. Itd be the same thing here. Top off the battery at home or work, and for the short trip that the average person does, youd do just fine, even better with an aux battery.

I really do think some kind of monitoring is best, so you dont get it so low that you wont get the car started if you shut it off, or end up really shortening the life of the battery by draining it way down a lot.

I wonder about even some sort of pulse width circuit one could make for the field coils, like charge for 10 seconds and stay off for 50 seconds, adjustable based on current draw from the battery. (Pulse and glide for your alternator!) Might be able to be done with a 555 timer but Im not real good with electronics. Maybe even too with a relay controller like Siemens Logo or AB Pico, or with a pulse timer controller for dust collectors. Just thinking of things Im familiar with at work.

I wouldnt run the alternator off the trans output shaft. Then if you get stuck in traffic, you might as well call for a tow truck now. Unless you leave your original and put in an extra one that runs off the output shaft, and switch field coils as needed.