Ok Ive been having problems starting my car since ive its come out for the summer. Ive think ive narrow it down to my battery. but i dont know.

See My battery is only two years old. If i have it in my winter car that car will start up, but when its in the REX it will not start it. THe car tries to start but then then theres not enough power to get it goin. But when i get a boost the car will start right away. Then when the car is warm up and if i leave it for a hour and go and start it, it will start. which confuses me.

I tested the batt with a volt meter it reads 12.9V then as a crack it over the batt will go down to 8V. is this normal or not?

 

Best place to start would be to clean all connections at the battery, fusible links, and starter. Check both positive and ground wires. 7s are notorious for this....

 

already did that.... all connections have been check

 

My guess would be old battery cables. Go get some heavy duty battery cables and I bet that solves your problem.

 

I'm with Rotor. These cables are 20 years old. Cut it open and I bent your cable has oxydized and is a greenish color on the inside. This will cause less current to flow. Thats why your boost is getting the job done, more current.
Do a search on battery cables. I did a write up on the replacement of the power and ground wires.