Broke down tonight ...

So I'm in Burger King's drive-thru and I realize my wipers (on the super fast setting) are moving super slow. My dash lights are also very dim. I get out on the main road and this big F-150 pulls up next to me honking its horn, so I figure by now my headlights are out. The car is now bucking wildly and my battery guage is all the way at the bottom. The car shut off (while I'm still moving) and I pull off to the side of the road (barely) and shut it off. 4-ways don't work either. Luckily my buddy drives by and stops so him, my roomie and I push the car while this girl who came to pick us up steers it off the road. Good Sam's (similar to AAA) couldn't find anyone to tow it so it has to sit until morning.
I figure it's the battery (~3 years old and the guage was real low) but it was POURING all night so my buddy thought maybe the alternator somehow got wet. Any suggestions? I'm hoping it's the battery because that is obviously cheaper. How long would a battery typically last? I replaced it when I bought it.
Good Sam's consultant said no companies were answering their phones or said it was "out of their range" ... probably just didn't want to do it with the weather, I don't really blame them, it was ugly tonight. Sorry this is long.