What would cause dash cluster to go "dead" when I hit the breaks?

My wife called me and said the "little
battery light" was on in her 2010 Accord.  
The battery itself is 2 years old so I
assumed her alternator was bad.  She
pulled over and said at low speed the car
"didn't want to go."  I had the car towed
to my home.  I went out and attempted
to start it and just got a click as if the
battery had insufficient charge.  I hooked
cables up to my truck and her car
started right up.  I unhooked the cables
and allowed her car to run for a few
minutes.  I then sat in the drivers seat
and applied pressure to the break to shift
the transmission into drive.  When I
pressed the break the gauge cluster
went dark and the tach dropped to zero
as if the car was completely dead.  Then
the cars idol seemed to slow and the car
died.  I repeated the process above and
again upon depressing the break pedal
everything went dark.