Okay here's the story.

Car has needed about 10 jumps in the past 2 years. Driven almost everyday, but only for 2 miles most of the time with a single 80 mile round trip once a week.

Replaced the battery 2 weeks ago. After one week, new battery needed a jump 3-4 times in a single day. It was around 20 degrees that day. Same day car dies while on the freeway. Jumped it again and got it to a friends house nearby. Few days later, I swapped out the new battery for the Optima Red Top from my Mustang. Got both car's home with no problems. Had the new battery tested and it checked out fine and has been in my Mustang for a week and hasn't shown a single sign of trouble.

Red Top in Focus hasn't shown a sign of trouble either.

I've tried the following to test the alternator. Remove negative battery cable while car is idling. Car stays on. BUT, if I then turn the headlights on, car immediately dies even if I'm revving the motor.

Battery light in the Focus has never come on.

 

Sounds like it's your alternator. Almost exact same thing happened when my alternator went for the second time. See if you can get it to a garage or auto parts store that'll test it for you. It should be a free test that takes all of thirty seconds.

 

That was my plan this weekend, but about an hour into trying to get it out I realized it was pretty much impossible. Its down in the bottom of the engine by the fire wall. I had already moved the steering and coolant reservoirs as well as the exhaust heat shield only to find out you have to under a motor mount and lift the engine up to wiggle it out of there. I figured I could get it out, but probably would be able to get it back in.

We'll see how long it runs with the Red Top in there. If it dies again its going to a shop.

 

Depending where you live, you might be able to drive the car to a mechanic/store that can test it while it's on the car. I've never had an alternator tested off my car as I only live two blocks away from a Fisher auto parts store.