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...................