Check charging system

Persistent problem. Info Center
often but not always indicates
"Check Charging System" .    
Somtimes but not always this
indicates when car is started. It
almost always goes away after
2 or 3 minutes upon starting to
drive, but persists more when
just idling. Other info: When this
first started, it more often
stayed with Check Charging
System notice staying on for
the duration of the drive. I had
alternator checked, indicated
that it was not charging. On 4
occasions the car just died
while driving, but putting it in N
and coasting for a few seconds
the car would start again no
prob. every time. Replaced
alternator. Drove away from
shop. 20 miles later, ALL lights,
dashboard indicators including
gas and temp gauges, AC,
radio, go out windows won't roll
down, doors won't unlock or
open. But the car is still running
and drivable. Transmission
works. I turn around, drive 20
miles back to the shop in this
condition. One block before the
shop, everything comes back
on and I roll down a window,
then everything goes out again.
Two more alternators later that
day and things seem to work.
But charging indicator
problems persist. I notice that
the indicator goes off and
comes on sometimes at idle
when some relay clicks and idle
speed increases or decreases. I
have throttle relay repaired for
separate issue and problem is
cured for a few weeks. It still
happens about a third of the
time when starting. I am
baffled. Alternators
occasionally show low charging
level when tested, and then
return to normal. Please advise.
Solution or diagnostic
suggestion. I have been through
at least 5 mechanics, two of
which are electrical specialists,
and have been to the dealt 3
times. Please advise.