99 Grand Marquis stumbles and sputtered help please

Hello,
I got a 99  Grand Marquis LS with 80.000 miles and we got the car for $2200
which  I felt was a great deal, I drove the car over 300 miles before we
decided to buy it, and no issues during the drive..

This is now day 3, and tonight all the sudden the car hesitated badly, the
battery light came on and then the car seemed to correct its self and the
battery light went went off, and then it drove ok, with NO other lights on like
check engine ect...

Well that scared the friend that drives it this car has had alot of work done
from what we can see and are worried as to what could cause the issue, She
drove it about 5 miles after all this started and it seems ok


now but we are quite concerned,

We know about the bad design of the intake manifold ( plastic) but we still
took a chance because of the condition and low mileage  Tomorrow it goes to
the shop we know and trust.although the mechanic has not seen it yet he did
say these 4.6 v8s are notorious  for that and he feels its a voltage issue,
something caused the voltage to go haywire. I just hate facing all this only 4
days after buying it.. I thought for sure a day spent with it and 300 miles
driving on and off the freeway would have showed issues guess I was wrong
on that one!! I still feel its a great car, I just wish these issues were in the
past.........