Low charge when hot.

Here's the thing. Depends. If you don't have EFI or some other critical electronics, your car should run off the battery for HOURS. When I first trunk mounted the battery in my 70RR, I did not realize it had been sulfated (discharged and sat at a dealer for a month). Coming back to San Diego from Vegas one weekend, "we had fumes." I knew it always held the needle a bit past zero. So we just unplugged the VR and drove it.........for HOURS. No radio, no blower/ heater, just the engine ignition and occasional brake lights.

Now of course this does not mean you don't have something wrong.