[911monty]

Okay. If I have this straight and you had the battery charged but it was dead again today, then you Could have a bad cell in the battery that is drawing the others down, or a continuous drain with the key off.
These are only possibilities since apparently the trickle charger was able to fully charge the battery, meaning drain is less than 4 amps.
Of course all this could have been caused by a bad alternator. Now I said test the fully charged battery, since that was the last known state, but you can do the same test I mentioned. Just use the current battery voltage as base, start car and see if voltage rises.
If you install a new battery you could maybe drive during daytime using no lights 2 hrs each way before low voltage causes problems. However a dead cell or current drain and all bets are off. Of course the starter, radiator and ac fans will all kill the battery.

I wouldn't recommend it. Sorry