How new a vehicle is it?
present day vehicles have onboard systems that constantly cycle on and off during the day causing a drain on the battery, after sitting for 7-9 days the battery may be too week to start the engine, the way the Chevorlet Tec stated that its best to run the vehicle every day, a minumum of once a week to keep the battery charged, its a design flaw of ereally new vehicles.
Ford Alternators (externally regulated) are exactly whats mounted on allot of small aircraft, As I remember with them battery abuse or a old bad battery, causes a undue strain on alternator, also bad cable/wire connections, a momentary short to ground on the field wire will mess up the voltage regulator, most times it kills the Voltage regulator, sometines it burns out one the diodes on the bridge, after 4 alternators one can pretty much guess its not the alternators fault, its somewhere on the chassis,
check the ground strap that is directly connected to the engine from the frame, otherwise its grounding through cables/linkages and wire shielding in order to supply ground for the alternator.
I'd once seen the throttle cable on a Cessna seize/ weld it self because of a mechanic failing to reconnect the ground strap to the motor mount, as the alternator was traying to get ground any way it could.
Corroded Ground connections
A quick way to find out if your alternator Field is working is turn on the ignition switch (dont start the engine) this will energize the alternators field which is a electro magnet so the alternator drive pulley will be magentized (field is working) a hand wrench (other steel item) should be drawn to the magnetized pulley.
A bad field circuit to the alternator, the drive pulley wont be magnetized, no field is mainly a regulator failure issue not a alternator issue.
Is your drive belt tensioned correctly? you shouldent be able to slip the pulley with the belt tensioned, if you can grab the pulley by hand and get it to slip even a little bit, The drive belt is not tensioned correctly.
