F150 Won't Start Again

My 1996 Ford F150 4.9L, IL6 cylinder had a corroded positive battery connection. Needless to say it created power loss and my truck wouldn't start. Disconnected cable cleaned what I could to get decent connect and got it started. The positive terminal connection was trashed, replaced it with new cable starts right up about three or four weeks without hesitation. Then one morning on the way to work it hesitates and audibly starts a little slower than normal so I revved it a little thinking the battery may be a little low. (I have to turn headlights ON to start truck security sys. BS) When I leave work it started, but now a little slower. Afraid the new cable was corroded I looked under the hood when I got home and they still looked brand new and had no abnormal heat on battery or cables. It started three more times gradually getting slower. Now it won’t start. When I try, no sound the lights (ALL) just get dimmer. Even connected to a battery jumper nothing. Also checked the neg. terminal, cable, and connections to the body and engine. One thing I noticed while inspecting the battery was that although both terminals were nice and clean looking, but underneath the cap on the side closest to the positive lead there was white-ish buildup around the three-hole plugs (in the bat. cap). I tried removing it cleanly away from the holes and off the battery. Once cleaned noticed the center hole was warped/sunken (a small amount) in about 35-40% of edge. Under cap neg side clean. Water levels fine. Still no start. checked fuel cut-off switch, fuses. Any ideas, suggestions, Help??? Could it be the starter motor? Just the battery?

First guess would be the battery. Bad cell, it sounds like, from your description. Second guess is gonna be the alternator. They can go bad in an instant, or slowly fade away. Take the battery to your local autoparts store and have them test it. The machine will tell you immediately if it's a bad cell.

Peace!

-Lou