The full charge idle voltage (I assume it was idle… it was just hooked up to the diagnostic machine, not bearing any load)was 11.5-11.6. Is that normal?
Idle means the engine is running without any depression of the accelerator pedal. If you’re describing a test with just the battery and the tester, no car, the term idle would not apply.
If that voltage was from a traditional battery load test, it’s an excellent result. If the testing machine was doing something else, I don’t know what it means.
A fully charged battery has a rest voltage of 12.6. In the car, engine running, I expect to see 13.5-15.0 with a functional charging system. It should hold a voltage in that range when idling with moderate load (headlights on, blower on high). Voltage of 11.5 or so in the car with the engine running means there’s no charging, almost always a faulty alternator.
A fully charged battery should easily start the engine and keep it running for 5 miles. I’ve seen some go well over ten times that distance.