Your battery has broken connections internally. To prove it, take it out, put it on a battery charger, and when it's charged check it with a discharge tester that puts about a 125 amp load on it and reads the voltage. Your local Oreilly's can do it for you. Just be sure you do the test outdoors and with eye and ear protection. You might blow the top off the battery.

Or just go get a new battery. Then get a multimeter and diagrams, or some educated help and solve the original problem.