I believe that it has something to do with a "high" draw computer. Plus the
fact that it has been three weeks sure isn't helping any! Your computer is
always active, thus constantly drawing power from your battery. I think that
Ford has the high draw computers. I work for the airlines and have seen it
all too often, the pilots go off for a week or so and come back only to have
to have their cars jumped because of dead batteries. If I can think back
enough I would be willing to bet that alot of those cars and trucks were
Ford products.
Aside from that you probably have a digital clock as well. It all adds up,
especially over a few days time. I would suggest that if you don't drive the
vehicle often enough to maintain the battery charge I would at the very
least start and run it for a bit every two days. Or, you can purchase a
trickle charger that will maintain the battery at optimum levels. Make sure
the charger that you purchase is NOT a manual charger as this you would have
to turn it off to avoid overcharging. I would say just buy the one that says
its an automatice charger.

Searcher1

My neighbor asked for my help with a similar problem. His new van ran its
battery down when left for a couple of weeks. He took it back and they
replaced the battery under warranty.

This new battery also dies when left just the same as the old one.

I took off a battery lead and put a current meter in the circuit. The
current was in the 100mA (or one tenth of an amp) range. This would take
about 3 to 4 weeks to drain a 50 to 75 amp/hour battery.  We removed other
power drains from the circuit by pulling fuses, so we killed the clock,
radio etc. We concluded it was the computer and I left him armed with too
much bad information to go back to the dealership.

They tested the battery and concluded the second battery was also bad! How
likely is that?

When asked about the computer they pointed out that when initially powered
up it will draw full current but after a few hours it goes into an idle mode
and only draws micro-amps. So the poster who suggested 20 to 30 milli amps
is correct..... this would take over 10 weeks to flatten a 50 amp/hour
battery.

I suggest that you charge the battery and drive to a Pep Boys or Batteries
USA or where ever they have a free curbside battery test. They will put a
load on it and see how much the Voltage drops. This is about the best way to
test it.

David
Raleigh