Starting issues

The other day ole blue wouldn't start (wouldn't crank over). I threw the battery charger on and it showed a very low charge. I charged it all day and it barley started. I drove on the freeway for a bit just to warm up the motor and charge the battery a bit more. When I got home I turned off the truck and went to restart and nothing... The motor wouldn't even turn over, I threw the charger back on and the battery was dead.
The battery was swapped out for a new one but still no start. I pulled the starter motor, this entailed hours of scraping away sludge, soaking the bolts, a breaker bar,  a handful of extensions, a 12 point 10mm socket (not 12 point 3/8'' I tried for a quite a bit) punching the frame, motor and front axle as they broke loose and it was off. I took it in to auto zone for testing and left with a new one. After all this nonsense she fires up right away!