Alternator problems 94 blazer?

i have a 94 full size chevy blazer with a v-8. the battery started losing voltage a couple days ago so i put a charger on it and it lasted two days. a couple hours ago, i drove it down the street and on the way back after ten minutes of driving it started acting funny at the stoplight and almost died. i made it home and sitting in the driveway at idle, the speedometer started bouncing between 50 & 60 mph. now it won't start. bad battery? bad alternator? sounds like a short somewhere. any suggestions would be greatly appreciated. thanks.