1974 Plymouth Duster Electrical Problems when hot

Hey Guys, I have a 1974 Plymouth Duster with a 318 and 904 Automatic Transmission. I acquired it in February and have been getting it road worthy since. Yesterday I went for a 'shake down' on the car before taking it to get the car inspected and while accelerating and got to about 30 MPH the car just died on me. I pulled over and tried to crank but the battery was completely dead. I waited about 10-15 Mins and then the engine cranked over and started (the cranking was slower than usual). I was limping it back home and not pressing on the gas much just letting it coast but it would still die and I would have to wait again to try and crank. The temperature was reading at 180 during this time. When I finally got it back home, I let the car sit for 30 mins and while cranking I was checking the battery and it was dropping to 6-7 Volts. Also the positive battery cable was super hot. All wiring is original and the distributor is electronic not points. If anyone has experience with this issue or can help in anyway, it would be greatly appreciated!
P.S I did not see a ground strap from engine to frame or on the heater box so I will try there