1997 Chevy Blazer Battery will not hold charge and engine w

I recently asked a question , I thought my computer was bad cause when I coded my car it would say "failed"< I used an actron code machine(OBD2 Pocketscan)I changed the computer, and Tried to start with no result, my gages do not move when the key is turned, But THe battery was completely dead , I jumped the car and was there an hour and never got enough juice to get a good crank out fo the car. How much voltage does it take to make everything go? Does the fuel pump require a certain amount of volts to run? Am I leaving anything out, when THe car stopped running, before it finally broke down, youd be driving down the road and al the dash light came on and there was a lull in the engine operation and then it seemed to snap back to normal, I havent ever had anything like this happen before. Continued the starter engages but is slow due to low volts.