Dead 2005 Chevy Venture

Hello everyone......
Seasons greetings and happy holidays to all!!
Las week I  went out driving during the weekend.
Parked my car at the Mall and when I came back 5 hrs later and tried to start
the car.....it was D.E.A.D. dead!!!
No power, no dash lights, nothing! Just a click when I tried to start the car.
I thought the bat may be dead. So I called my insurance for a boost.
The man arrived, gave me a boost and about 5 to 10 min after, the car died
again. So he gave me a boost again, and this time within 3 minutes or so the
car went DEAD again.
At his time the gentleman helping said it was not a batt. issue and that I
should have the car towed.
The following day after the tow, I took out the Batt and took it to get tested,
the result was that the battery was fine. (As it should have been, since the
bat and Alt are new. Less than 6 months)
Now having said all that, I would like to know if anyone can point me to the
right direction as to what can possibly be wrong.
I live on a very tight and low income, so if I can fix the problem myself, I
always try to. Besides I'm good with mechanical work and I like to learn, so I
do the research and watch the videos, and if I think I can do it myself I do.
if not, then I'll look for the correct person for the job.
I would like to give it a shot myself due to financial reasons, but I do not
know where to start.
Alternator fuse? Fusible link? I know it's electrical related, or at least I think it
is.
Help please. Im paying insurance to keep my car parked on the street. I live
in NY and don't have a driveway and can't afford storage, and most
important.......I like my Chevy Venture!!
Thank you all once again.
Alex.