1996 cutlass supreme starting problems

OK, I'm having a bit of a problem with my 96' cutlass.

It all starting on friday while driving home from work. The radio stopped working, and then about 2 minutes later the car just died. I was driving on interstate going about 60 and it just shut off, so I pulled over. Tried turning key over, nothing. No lights, everything dead.

Since it was late called a buddy and we towed it home. Today I starting taking a look at it, and I'm stumped.

The battery is fully charged at around 12.5 volts. When I turn the key, nothing happens. The speedometer goes crazy and moves up and down, that I thought was strange.

Also, there seems to be no power going to power locks, windows, and windshield wipers. The wipers have barely enough power to move, along with the windows and locks. The window is very slow to go down, compared to normal.

Does anyone have any clue as to what is going on?

1996 cutlass supreme SL 3.1L

Your battery is dead because your alternator stopped charging. Have you tried a jumo start or checked the voltage at the battery with the key in the crank position or with the headlights on?