Car not starting

Okay, so it will not start without a jump. Have the battery load tested. Then take your jumper cables and connect them to the battery and the ground to the engine block and positive to the same lug the battery connects on the starter. Will it start now? If so you have a bad connection. Cables and terminals like to corrode inside the cable insulation. They look good outside but are actually not any good.

So when you first try to start it what does it do? Loud click, chatter or nothing? If you turn the headlights on, do they come on? What do they do when you turn the key? I'm just trying to figure out if the battery is very low as a result of a parasitic draw (interior light staying on or module not shutting down)and requires a jump for that reason OR is it something like a high resistance in a starter relay or starter motor that the higher current of the second battery helps overcome.