I think it would be pretty unlikely that the Auto shop would get
a good and charged reading on your battery if it was actually bad
and discharged.

One scenario is that the cables to your battery or their connection
at the terminals (on either side) were not working. When you shut
off the engine the battery gave no juice to raise your motor. When
you connected the jumper battery you got a connection from it and
got your juice back.

I'll bet it's connections.

Get a cheap meter at Radio Shack or the autoparts store. See if the
Altenator
is putting out any voltage. Check your batter at various point in the day.
You'll
learn some things.

If your cables are really bad replace them. More likely it't just that the
ends
need to be cleaned up. Get one of those little brushes that are made both
the clean the post on the battery and the connectors that go on them. I
also
keep a little tube of dielectric greese. It seems kind of expensive when you
buy
it, but that little tube goes a looong way. Put a little grease on all your
terminals
and if there is any exposed parts of wires (which there shouldn't be, but
sometimes
there is).

Good Luck.