How do you check diode pack and battery terminals?
I have not mentioned the battery terminals.
I`m going to assume the connections are good, as the car starts.
If the diode pack was blown, normally the battery light on the dash glows dimly, with the ignition turned off, though you can check for a ground to earth with a multi meter.
Make sure you have 12v with the ignition on at the exciter wire (yellow arrow), and large red charge wire (red arrow) can corrode through.
As I said, I would expect a fully charged battery to run the car for at least 30 minutes, even if it was not being charged.
From what you have said, you are starting the car with jump leads, so the battery cannot be fully charged, what voltage is it holding?